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lEduratiattal PfiyrliiilDgg mmtngrapliH 

This volume, which is No. 23 in the Series, 

was prepared under direction of the faculty 

of New York University. 



PERIODIC VARIATIONS IN EFFICIENCY 



PERIODIC VARIATIONS 
IN EFFICIENCY 

As shown in Mental and Physical Tests together 
with some Weather Effects 



By 

ARCHIBALD G. PEAKS 




BALTIMORE 
WARWICK & YORK, Inc. 

1921 



.P4 



Copyright, 1921, by 
WARWICK & YORK, Inc. 



2)CI.A630352 



PREFACE 

Many studies have appeared which suggest the existence 
of periodic variations in both physical and mental activities 
during the year, during the day, and in conjunction with 
periodic changes in natural phenomena such as sunlight 
and temperature, but as yet the factors involved are but 
little understood. In order to assist in the solution of these 
complex problems, the author has attempted the following: 

(i) To give a complete historical view of the experi- 
mental data on the subject. 

(2) To examine the means, methods, and procedure 
employed by other investigators. 

(3) To give a critical evaluation of the results of pre- 
vious investigations in the light of the means em- 
ployed, the methods used, and the procedure fol- 
lowed. 

(4) To use improved methods and procedure in investi- 
gating the problems of periodicity. 

(5) To summarize the results of previous investigators, 
and compare them with his own. 

(6) To point out some problems which future investi- 
gators should attempt, and some errors which they 
should avoid. 



.s 



f« 



CONTENTS 

Preface t 

I. Growth Rythms ~ 

II. Seasonal Periodicity in Mental and Physical Abilities 

I— Periodicity of Attention (Schtiyten) 9 

2— Periodicity in Muscle Strength (Schuyten) .' 13 

3— Periodicity in Primary Memory. (Lobsien) 15 

4— Periodicity in Strength and Endurance (Lehman 

and Pedersen) ig 

5 — Seasonal Variations in Diurnal Periodicity (Kuhnes) 25 
6— Summary of Problems and Results in Seasonal 

Periodicity ; _ 27 

III. An Original Experimental Study in Seasonal Period- 

icity 

I — Introduction \ 29 

2 — Periodicity as shown in Physical Tests 29 

3 — Periodicity as shown in Primary Memory Tests 33 

4— Comparisons of Mental and Physical Seasonal 

Periodicity 36 

IV. Diurnal Variations in Efficiency 

I — Introduction " ^g 

2— Daily Variations in Voluntary Muscular Contrac- 
tion ( Storey) , 4g 

3— The Diurnal Course of Efficiency (Marsh) 50 

4— Diurnal Variations and Exercise Effects (Lehman 

and Pedersen ) ^2 

5— Diurnal Variations in Muscular Energy (Kuhnes) 53 

6 — Variations in Efficiency During the Day (Gates) 54 

7 — Diurnal Variations in Memory and Association 

(Gates) 57 

8— Summary of Problems and Results in Diurnal 

Periodicity 9S 

9 — Diurnal Periodicity in my Orginal Experimental 

Investigations 59 

V. — Other Periodic Variations 

I — Introduction 61 

2 — Twenty-eight Day Periodicity 61 

3 — Twent3^-three Day Periodicity 62 

4 — Weekly Periodicity 63 

5 — Weekly Periodicity in my Original Experimental 

Investigations 64 

3 



4 CONTENTS 

VI. — Weather Influences 

I — Introduction 66 

2 — General Weather Effects 66 

(a) Conduct and the Weather (Dexter) 

(b) Civilization and Climate (Huntington) 68 

(c) Effects of Weather on Ability to Learn 
(Lehman and Pedersen) 6g 

3 — Effects of Variations in Sunlight 70 

4 — Effects of Changes in Temperature 70 

(a) Influence of Temperature on Rapidity of 

Addition (Lehman and Pedersen) ']2 

5 — Effects of Variations in Humidity 'j}, 

6 — Effects of Barometric Changes 74 

7 — Summary of Problems and Results in Weather 

Effetts 75 

8 — Weather Effects in my Original Experimental 

Investigation 1^ 

VII. Critical Review of Experimental Methods in Investi- 
gating Periodicity 

I — Introduction 82 

2 — Detailed Discussion of Scientific Method 83 

3.— Validity of Results _. QO 

VIII. — Summary and Suggestions 9i 

X.— Bibliography 94 



CHAPTER I. 

GROWTH RHYTHMS 

All human life is a growth involving numerous mental 
and physical changes in the human organism from hour to 
hour, day to day, month to month, year to year, and age 
to age. This growth was long considered to follow a quite 
regular course from year to year, except in individual cases 
when its course was interrupted by sickness, poor food, 
mal-nutrition, worry, or some other like cause. We find, 
however, a vague but more or less real recognition of the 
more general periodic changes in human life in Hippocrates' 
division of life into seven stages, a division which was 
later employed by Shakespeare in his "Seven Ages" of man. 

These general divisions continued to be recognized for 
several centuries, though the depth and profundity of the 
changes taking place, (especially between infancy and 
childhood and between childhood and youth), were but 
vaguely comprehended. It is only with the growth of 
scientific research along the lines of Biology, Genetic Psy- 
chology, Child Study, and Experimental Pedagogy that 
their great significance has been sufficiently recognized. 

Besides these, many other growth rhythms have been 
detected. As early as 1859, E. Smith^^ showed in his 
"Analysis of Respiration" that breathing is at a maximum 
in spring and at a minimum toward the end of the summer 
and beginning of autumn. 

Somewhat later, N. Finsen^^ found that the amount of 
haemoglobin in the blood also has periodic variations, show- 
ing a maximum in fall and a minimum in winter. This 
might be explained partly by the corresponding increase or 
decrease in the amount of air breathed; as the maximum 
amount of haemoglobin comes sometime before the mini- 

5 



6 PERIODIC VARIATIONS IN EFFlCIIvNCY 

mum of breathing, while the minimum of the former shows 
itself a short time before the minimum of the latter. 

Following this, Lehman^^ through tests with a plethysmo- 
graph found that there are periodic variations in the strength 
of heart beats which agree with the variations in the haemo- 
globin content of the blood, in being greater in summer than 
in winter. 

That the growth in height and weight of the child under- 
goes various periodic changes within the year was first dis- 
covered by Malling-Hansen, director of the deaf mute in- 
stitute in Copenhagen. The occasion for its discovery was 
accidental. In the year 1882, Malling-Hansen changed the 
diet of all the boys under his care, and in order to discover 
the effects of this change on the physical development of 
the pupils, he hit upon the expedient of carefully weighing 
the boys daily. This he did with 130 boys from May, 
1882, to Feb., 1886, and for the last two years of that period 
he also measured them daily with much care, taking elabor- 
ate precautions to secure accuracy and uniformity in all 
measurements. By this means he discovered that the height 
and weight of growing boys seemed to be subject to periodic 
variations which recurred year after year in the same 
manner. 

Nearly all his tables in "Perioden im Gewicht der Kinder 
und der Sonnewaerme"^^ are based on the measurements 
and weighings of about 70 boys, from nine to seventeen 
years old, weighed from May, 1882, to Feb., 1886, and 
measured from Feb., 1884, to Feb., 1886. The children 
were weighed four times per day with the exceptions of va- 
cations, each of which lasted six weeks, from the middle 
of July to the end of August. The pupils were weighed in 
groups of sixteen to eighteen, and the heights given are also 
of these groups. His data, therefore, show nothing as to 
changes in individuals. His results may be summarized as 
follows : The weight of a group of growing boys from nine 



GROWTH KHYTHMS 7 

to sixteen years of age, has three periods of growth during, 
the year, — s. maximal, a middle, and a minimal. The maxi- 
mal period begins in August and ends in the middle of 
December, lasting four and one-half months. The minimal 
period extends from the end of April to the end of July, last- 
ing three months. During the maximal period, the rate of 
increase is three times as great as in the middle periodl 
Almost the whole weight gained in the middle period is li^st 
in the minimal period. 

Respecting growth in height, he finds that the minimal 
period begins in August and lasts till the middle of Novem- 
ber, three and one-half months. The middle period reaches 
from the end of November till the end of March, about four 
months. The maximal period extends from the end of 
March to the middle of August, about four and one-half 
months. The daily rate of gain in height in the maximal 
period is two and one-half times as great, and in the middle 
period is twice as great as that of the minimal period. 

It is also interesting to note here that Dr. Winifred Hall, 
of Haverford College, develops the same law of separate 
rhythms for height and weight during the larger periods be- 
fore and during pubescence that Malling-Hansen found 
for the seasons. Dr. Hall finds that when the vertical dimen- 
sions of the body are undergoing acceleration of their rate 
of growth, the horizontal undergo a retardation of their 
growth, and conversely. The same author also claims that 
growth in height is due largely to an increase in length of the 
long bones. G. Stanley Hall claims that adults tend to grow 
thin when children grow tall, and to grow thick when chil- 
dren grow heavy; and suggests that by using the former 
period for cures, fleshy people can aid nature. 

Many other annual or seasonal rhythms of life are known 
to science, among the more common of which we find the 
migration of birds, the hibernation of various animals, the 
running of fishes, the shedding of winter coats of fur and 



8 PERIODIC VARIATIONS IN EFFICIENCY 

feathers, and the mating season of animals of all sorts. 
We see, therefore, that Malling-Hansen was in the presence 
of a great biological law of rhythmic growth which depends 
for its existence on the very nature of the universe itself. 
The findings of Malling-Hansen have been corroborated 
in the main by Dr. Schmidt-Monnard in Halle, Germany. 
Besides this, various supplements to these investigations 
have been made, regarding the periodicity of mental and 
physical development, and the periodic changes in mental 
and physical abilities, which seek to discover the nature of 
any existing paralellisms in physical and psychic functions 
and to discover the probable causes of their periodic varia- 
tions. A full account of such investigations will be given in 
the following pages. 



CHAPTER II. 

SEASONAL PERIODICITY IN MENTAL AND PHY- 
SICAL ABILITIES. 

I. PERIODICITY 01^ Attl:ntion. (Schuytkn) 

(i) Method. During the school year 1893-4, Dr. M. C. 
Schuyten, director of the pedagogical laboratory at Antwerp, 
made a series of investigations concerning the periodic 
variations .in the power of attention. The following data 
are taken from a report of his work given by Marx Lob- 
sien in his "Schwankungen der Psychischen Kapazitat." 

Two upper and two lower classes of boys and girls from 
eight to ten years of age were tested monthly to discover 
any periodic variations in their power of attention. The 
children were tested four times on each test day. To avoid 
any disturbance from other classes, those to be tested were 
isolated during the tests. 

Each child sat with his Flemish reader open before him. 
At a given signal which always remained the same, the chil- 
dren began to read silently. The experimenter noted by ob- 
servation those who were not attentive, those who stopped 
reading, those who raised the eyes from the pages, and 
those who were continuously attentive through five minutes, 
the length of the test. The investigation was begun in 
March, 1893, and continued for one year except during the 
months of August and September, when the long vacatioi 
intervened. 

(2) Results. The general summary of the results for 
the year is here given : 

Month Jan. Feb. Mch. Apr. May. Jun. July Oct. Nov. Dec. 
Per cent, of 
Attention 
Energy 68 63 yy 69 64 42 27 48 62 6y 

9 



lO PERIODIC VARIATIONS IN i:i^:FlCIE:NCY 

He notes the greatest difference between March and July. 
Upon these results he bases the following conclusions : 

1. The power of attention in children is inversely pro- 
portional to the atmospheric temperature. 

2. It is greater in the higher than in the lower classes. 

3. It is greater in girls than in boys. 

4. It diminishes from 8:30 a. m. to 11:00 a. m., and 
again from 2.00 p. m. to 4 :oo p. m., but it is always 
greater at 2:00 p. m. than at 11:00 a. m., and less 
than at 8 :30 a. m. 

(3) Verifying Tests. In order to satisfy himself that 
the results were valid, Schuyten made a second set of ex- 
periments using the same general method of study as before 
with one exception, he began the tests in April instead of 
March. The final summary of the results from the verifying 
tests is here given : 

Month Jan. Feb. Mch. Apr. May Jun. July Oct. Nov. Dec. 
Per cent, of 
Attention 
Energy 59 54 54 51 45 42 35 4^ 51 57 

Various comparative tables are given some of which are 
here reproduced: 

TESTS TAKEN AFTER A REST 

Month Jan. Feb. Mch. Apr. May Jun. Jul. Oct. Nov. Dec. 
Per Cent. 

A. M. 64 59 57 55 47 45 39 52 55 62 

P. M. 59 55 57 52 49 47 42 50 51 58 

TESTS TAKEN BEFORE AND AFTER A REST 

Month Jan. Feb. Mch. Apr. May Jun. Jul. Oct. Nov. Dec. 
Per Cent. 

Before Rest 56 51 50 43 42 36 29 46 48 55 

After Rest 61 57 57 53 49 46 40 51 53 60 

TESTS AFTER REST, HIGH AND LOW CLASSES 
Month Jan. Feb. Mch. Apr. May Jun. Jul. Oct. Nov. Dec. 

Per Cent. 
High Class 61 56 55 52 49 47 4i 52 52 59 

Low Class 61 57 49 54 48 45 40 52 54 60 



SEJASONAI, PERIODICITY IN ABIUTlES II 

TESTS AFTER REST, BOYS AND GIRLS 
Month Jan. Feb. Mch. Apr. May Jun. Jul. Oct. Nov. Dec. 

Boys 6i 56 57 54 49 45 41 50 53 60 

Girls 61 58 57 53 41 46 40 51 53 59 

From these results Schuyten concludes : 

1. That the results of the first experiment are verified 
by the second, 

2. Rest has a good influence on attention. 

3. In winter, a higher per cent, is obtained after the 
morning rest than after the afternoon rest ; in sum- 
mer the reverse is true. This would show that inter- 
missions are more beneficial in summer than in 
winter. 

4. Recess periods have more influence on the lower 
classes than on the higher classes. 

5. Recess periods are more beneficial to boys than to 
girls. 

(4) Criticism. This work by Schuyten is a pioneer in 
its field and as such deserves great credit. There are sev- 
eral probable sources of error, however, on the basis of 
which we may question the universal validity of his re- 
sults. The first is in regard to the means employed. It is 
entirely probable that the pages used in the Flemish readers 
were not equally interesting to all the children in the diflfer- 
ent classes so that the material lacked uniformity. Schuyten 
himself admits that this may be true. 

There may also be a question raised as to the usefulness 
of the method of recorded observation in measuring the at- 
tention of children in a large group. The author judged 
only by appearances without checking the results by the 
introspection of the children. Aside from the fact that 
these results do not easily lend themselves to quantitative 
measurements, it is possible that many times only the signs 



12 PERIODIC VARIATIONS IN EFFICIENCY 

of attention were mistaken for the fact of attention. 
Schuyten had his doubts about this point, and Lobsien 
doubted so strongly that he devised a new method which 
aimed at uniformity of material, and gave a record which 
lent itself more readily to quantitative measurement. 

In regard to the results from Schuyten's "Verifying 
Test," I can scarcely agree with him that it proves the 
results of the first experiment. It seems to me that in 
Schuyten's first tests, we see in the high level for March 
the effects of novelty rather than a true index of the ability 
or power of attention. This shows the great need for pre- 
liminary tests in any experimental investigation in order 
to perfect the method, and to eliminate practice effects. As 
none were given, it seems reasonable to suppose that the re- 
sults of the verifying test give a truer range of the varia- 
bility of attention than do the results from the first set of 
tests. These later results seem to show a crest in January 
rather than in March. 

Concerning his conclusions for age and sex differences, 
though we grant the validity of his results, the resulting 
differences are not large enough or persistent enough to 
be the basis for any such general conclusions as he has made. 
Final] V, Schuyten is not warranted in drawing any such 
sweeping conclusions from four tests made on the same 
day, and once each month. The work of other investigators 
shows that the records from such a small number of tests 
per month contain many accidental errors which tend to 
minimize the validity of the results, so that what seems to be 
seasonal variations may be due in a large part to accidental 
causes. 

The results from these experiments are shown graphically 
in Fig. 2, where they are compared to his results on period- 
icity in muscular energy. 

2. Periodicity in Muscle Strength. (Schuyten) 
(i) Method. Schujten next tried by experiments to 



SEASONAE,. PT^"RTOt)lClTY IN ABltlTlKS r3' 

discorer the: aninual variations in and the annual increase 
of muscle' strength in boys and girls. Accordingly he tested 
the grip strength of a group of children of both sexes in 
Antwerp during the school year from October, 1898, to 
July, 1899. These tests were given on the fifteenth of each 
month at 2:15 p. m. In all 5400 results were tabulated. 
The Elliptical Dynamometer was used for both pushing and 
pulling tests, first with the right and then with the left hand. 
The children were encouraged to wager so they would use 
all their strength. 

(2) Results. The following table shows the results for 
both sexes, pushing and pulling : 

Month Oct. Nov. Dec. Jan. Feb. Mch. Apr. May Jun. Jul. 

Pull 438 469 487 491 511 490 515 534 558 58-' 

Boys 

Push 139 149 155 156 162 156 166 170 178 185 

Pull 439 436 452 453 486 481 481 481 488 506 

Girls 

Push 138 139 144 144 155 155 153 154 155 161 

Pull 436 455 469 474 497 486 499 509 ^24 547 

Both 

Push 139 145 149 151 158 155 159 162 t67 174 

One result which is everywhere shown is the downward 
curve of capacity in March, only one case showing a slight 
increase. Commenting on this the author gives the follow- 
ing table which shows the monthly increase or decrease in 
physical strength : 

MONTHLY INCREASE OR DECREASE IN PHYSICAL 
STRENGTH (Lobsien) 
Month Oct. Nov. Dec. Jan. Feb. Mch. 

Boys — 3.1 1.6 04 1.9 — 2.0 

Girls — C.3 i.o o.i 0.5 —0,5 

Average — 1.8 1.6 o.i 2.4 — i.i 

(3) Verification. Not wholly satisfied with these re- 
sults Schuyten made a supplement to them in the year fol- 
lowing. In this investigation he tried to eliminate the ef- 



Apr. 


May Jun. 


July 


2.6 


1.9 2.4 


24 


0.0 


0.2 0.6 


1.8 


1.3 


1.0 1.5 


2.3 



14 PERIODIC VARIATIONS IN Kl^FlCIENCV 

fects of growth and habit by testing a different group of chiU 
dren each month. In several pubHc schools of Antwerp^ he 
grouped the children according to the month in which they 
were born. Each child began the tests at the age of nine 
years and nine months, those born in January being tested 
in October, those born in February being tested in Novem- 
ber, etc. Each monthly group was tested three times during 
the first half of the month, first with the left hand and then 
with the right hand. The results from 45,453 records are 
shown in the tables below. These tables show the average 
pulling strength for both hands combined. The children 
in the first table were born in the year 1889, and those in the 
second table were born in 1890. 

1889 1890 



Month 


Boys 


Girls 


Aver. 


Month 


Boys 


Girls 


Aver. 


Jan. 


47.0 


38.4 


43-0 


Jan. 


39.9 


34.1 


36.6 


Feb. 


44.1 


38.7 


41.3 


Feb. 


38.4 


34.3 


36.1 


Mch. 


44.9 


36.0 


38.8 


Mch. 


35-9 


32.8 


34.3 


Apr. 


46.9 


37.9 


41.8 


Apr. 


39.1 


34.0 


36.3 


May 


47.0 


38.6 


42.7 


May. 


41.2 


33.9 


38.4 


Jun. 


50.6 


40.1 


46.0 


Jun. 


43.5 


35-7 


38.7 


Jul. 


49.9 


39.8 


44.4 


Jul. 


44-3 


36.4 


39.5 


Oct. 


44.1 


36.2 


39.1 


Oct. 


38.2 


32.6 


35.1 


Nov. 


457 


37.2 


40.9 


Nov. 


38.0 


33-1 


35.3 


Dec. 


46.S 


38.1 


42.4 


Dec. 


39-5 


34.1 


36.6 



From the results of these two investigations, Schuyten 
concludes that there are four distinct periods for muscular 
energy as follows: 

1. A falling period from January to March, 

2. A rising period from April to June, 

3. A decrease from July to September, 

4. An increase from October to December. 

(4) Criticism. Of these two investigations concerning 
periodicity in muscular energy, Schuyten bases his con- 
clusions almost entirely on the second or verifying test. Of 
course it is true that the effects of practice and of yearly 
growth are largely eliminated by this, and the results from. 



S^ASONAI, PKRiODiClTY tN ASlLltl^S t^ 

the different months are comparable. The only drawback is 
that the groups tested were not homogeneous or uniform, 
and the individual differences found might destroy the value 
of the most important variations shown in the results. 

While recognizing that this criticism might be made, 
Schuyten minimizes its effect, and entirely neglects it in 
drawing his conclusions. A series of preliminary tests 
made on the monthly groups might have been arranged so 
that the individual differences could have been almost en- 
tirely eliminated. That no such preliminary tests were 
given seems very unfortunate, and casts the only doubt on 
what is otherwise a very carefully conducted experiment. 
3. 'Pe:riodicity in Primary Memory. (Lobsie:n) 

(i) Method. Lobsien criticised Schuyten's conclusions 
on the grounds ( i ) that the tests were not homogeneous or 
of the same degree of difficulty, and (2) that the variations 
noted in the tests are not entirely due to changes of the 
seasons or to changes in the atmospheric temperature. He 
therefore sought to supplement and verify the work of 
Schuyten in a similar investigation. In gathering the data, 
experiments were made on boys and girls in the public 
schools of Kiel, Germany, from 8 to 14 years of age. They 
were made on the fifteenth day of each month from Septem- 
ber, 1901, to June, 1902, July and August being vacation 
months. 

(d) Procedure. Lobsien's work is limited to the study 
of primary memory for lists of ten words involving both 
visual and auditory imagery, which are here reproduced : 

LOBSIEN'S WORD LISTS 





VISUAL 




A( 




A 




A 


I. 


Sonnenlicht 


T. 


Gesang 


2. 


Fensterscheibe 


2. 


Gebell 


3. 


Wandteller 


3. 


Summen 


4- 


Handspiegel 


4- 


Sausen 


5. 


Himmelblau 


5- 


Rasseln 



i6 


PKRIODTC 


\'ARIATTONS 


IN KFI^TCTK 


6. 


Abendstern 


6. 


Lispeln 


7- 


Taubenhaiis 


7. 


Poltern 


8. 


Ofenschirm 


8. 


Larmen 


9. 


Turmuhr 


9. 


Donnern 


10. 


Bierglas 


lO. 


Sprechen 




B 




B 


I. 


Abendrot 


I. 


Drohnen 


2. 


Brieftasche 


2. 


Stamp fen 


3- 


Federbusch 


3. 


Krachen 


4- 


Fensterkreuz 


4. 


Bellen 


5. 


Feuerwerk 


5. 


Sauseln 


6. 


Handschrift 


6. 


Raiischen 


7- 


Mondscheibe 


7. 


Knistern 


8. 


Gotteshaiis 


8. 


Klirren 


9- 


Kirchtum 


9. 


Kreiscben 


10. 


Streichholz 


10. 


Blasen 




C 




C 


I. 


Kohlschwarz 


I. 


Ticken 


2, 


Morgenstern 


2. 


Weihern 


3. 


Nachtmut^e 


3. 


Meckern 


4- 


Olzweig 


4. 


Gackern 


5- 


Ofenraiich 


5. 


K rah en 


6. 


Rotfuchs 


6. 


Brullen 


/• 


Freimarke 


7. 


Klingen 


8. 


Angesicht 


8. 


Pfeifen 


9. 


Vorschrift 


9- 


Trommebi 


10. 


Lampenglas 


10. 


Klappern 




D 




D 


I. 


Feuerschein 


I. 


Zirpen 


2. 


Morgenrote 


2. 


Rufen 


3. 


Leuchtkeugel 


3. 


Weinen 


4. 


Postkarte 


4- 


Scharren 


5. 


Schattenbild 


5. 


Seufzen 


6. 


Blitzstrahl 


6. 


Knallen 


7. 


Georgine 


7- 


Puffen 


8. 


Spiegelbild 


8. 


Schluchzen 


9. 


Zifferblatt 


9- 


Winseln 


10. 


Hangenlampe 


10. 


Klopfen 



The word lists were spoken plainly after which each pupil 
was asked to write the words in a list at once. Lobsien tab- 
ulated the results separately for girls and boys and for each 
age. 

(2) Results. The results as shown in the accompanying 



SKASONAL PE:RI0DICITY IN ABILITIES 



17 



tables include 8900 records and the experiments are based 
on two important activities of the mind, primary memory and 



attention. The resul 


t are here given: 
GIRLS 






Month 


Visual Imagery 


Auditory Imagery 


September 


23S6 




251S 


October 


2489 




2138 


November 


3964 




2605 


December 


2686 




2257 


January 


2080 




2325 


February 


2810 




2322 


March 


2847 




2761 


April 


2483 




2262 


May 


2640 




2641 


June 


2523 
BOYS 




2530 


Month 


Visual Imagery 


Auditory Imagery 


September 


2328 




2492 


October 


2073 




1894 


Novembber 


2063 




2218 


December 


2142 




2243 


January 


2053 




2319 


February 


(1965 Estimated) 


(1968) 


March 


(2102 Partly lost) (2161) 


April 


201 1 




2266 


May 


2246 




2400 


June 


2384 




1967 



The curves for boys and girls are much alike. The mid- 
dle energy height is much higher for girls than for boys. In 
general these curves show a high period or crest around 
December and January, and a trough or depression in Feb- 
ruary and April. The visual tests show a curve which is 
higher in the first part than in the last part, a fact which 
he considers the more remarkable because the pupils should 
improve with practice. The acoustic curve for girls in 
general parallels the visual curve, but always has a smaller 
value. There is very little difference in ages, except that 
psychic energy tends to become more uniform with age. 

The results for boys show the highest value in the first 
tests in September, and at the end of the tests in June. A 



i8 pe:riodic variations in efficiency 

second slight elevation is found in January. The visual 
curve is nearly always less for boys than the auditory curve, 
and the variations are more opposite than parallel. Boys 
agree with girls in the depression in the visual curve around 
July. They also agree with girls in showing a high value in 
December and January and corresponding depressions in 
February and April. The first half of the year seems the 
best for boys. On the whole, psychic energy is higher for 
girls than for boys, but boys show a higher low point than 
girls. 

The table showing the monthly changes in psychic capac- 
ity shows almost a regular rise and fall for the months fol- 
lowing each other for the girls, while for the boys, the 
rhythmic changes extend over a somewhat longer period. 

(3) Criticism. The work of Lobsien while very care- 
fully worked over seems to be somewhat questionable both 
in the materials and the procedure. While the method was 
new, the word materials are so much alike in form that the 
memory images undoubtedly interfered with one another. 
A careful survey of the word lists will bear out this state- 
ment. Then again, there are so many accidental factors which 
enter into mental abilities, due to time of day, temperature, 
individual daily results, etc., that it is doubtful in the ex- 
treme that the results from tests made but once per niontb 
are a true index of any but accidental factors, and thit the 
seasonal rhythms cannot be discovered from tests taken but 
once per month. The mere fact that such a large number of 
persons was tested cannot overcome this source of error in 
the procedure. The validity of his conclusions that "Physical 
and physic development do not parallel," is destroyed by 
the errors in the data. 

4. Periodicity in Physical Strength. (Lehman 
AND Pedersen) 

(i) Aim. Lehman and Pedersen made a much more 
careful study of periodicity than either Schuyten or Lobsien. 



SEASONAt PERIODICITY IN ABIT.ll^iJ^S tQ 

By means of a long series of experiments they attempted to 
discover the effects of the weather on muscle strength. As 
the experiments covered a period of nearly two years, many 
of the data show seasonal variations. We will, therefore, 
describe the more general variations here, reserving only 
some of the details for the section on weather effects". The 
experiments were made partly on public school pupils in 
Copenhagen, and partly on three grown people. As the 
apparatus and procedure used for the children was different 
from that used for the adults, I will, describe the method and 
procedure for each group by itself. 

(2) The Individual Tests. Most of the individual 
tests were made by three persons. Dr. Lehman, Dr. Peder- 
sen, and Miss J^ Each used the same individual dynamome- 
ter throughout the tests, one being provided for each. As 
the dynamometers differed, no comparisons were made be- 
tween the results, these being referred to as I, II, and III. 
In the tests, each person always used his own dynamometer, 
Miss J. Ill, Pedersen II, and Lehman I. The tests were 
taken always with the left hand by Lehman and Miss J. and 
with the right hand by Pedersen, who was left handed. 
Five tests were made, with not less than thirty seconds be- 
tween, immediately after rising each day. 

(3) The School Tests. In the School Tests, five groups 
of children were used. 

Group I, consisted of twenty-one pupils between 12 and 
13 years of age. This group was tested one day (always the 
same day) each week, between 9 a. m. and 10 a. m., on each 
test day from January i to April 21, 1904. 

Group II, consisting of twenty-one pupils between 10 and 

11 years of age, were tested once each week as above from 
August 12, 1904, to March 31, 1905. 

Group III, consisting of eighteen pupils between 11 and 

12 years of age, were similarly tested once each week from 
August 12, 1904 to March 31, 1905. 



20 PERIODIC VARIATIONS IN RPFLCIRNCY 

Group IV, consisting of the twenty-one pupils between 
13 and 14 years of age, were tested between 9 a. m. and 
10 a. m. once each week from August 12, 1904, to March 

31, 1905. 

Group V, consisting of ten pupils between 12 and 13 
years -of age, were tested between 10 a. m. and 12 m. on 
each school day from January 12, 1906, to June i, 1906, and 
again from August 12, 1906 to December 21, 1906. 

In these tests, Lehman's Ergograph was used. The tests 
were carefully controlled and the children were urged to 
compete with each other for high records. Before taking 
the tests each boy was asked to dry his hand on a towel. 
Each boy then took four grips with an interval of four 
seconds between at a uniform tempo. The averages of these 
four trials are shown in the tables for results. Each boy 
used only his most dextrous hand in making records. 

Before the real tests, each boy was allowed to make a 
number of trials, so as to learn to grip in a uniform tempo, 
which was the same for all so far as possible. Whenever a 
pupil was absent, ill, or otherwise indisposed, or did not 
wish to grip (which happened very seldom), an average 
grip was worked out for him from the days preceding and 
following, and put in its place. Pupils who were absent 
for a long period were not included in tabulating the results. 

(4) Results. The more general of the results from the 
individual tests, are as follows : 

The curve of Lehman (who was 47 years old), "sinks in 
the fall to the middle of December, then rises, first slowly, 
then more quickly to the end of June. It sinks during July 
and August, rises abruptly in September, and sinks grad- 
ually to the end of the tests in December." 

The curve of Pedersen (who was 36 years old), is very 
"similar to that of Lehman during most of the time." 

The curve of Miss J. (who was 18 years old), and Group 
V of the bovs, who were also tested from January to Decem- 



Sl^ASONAI. PKRIODICITY IN ABILITIES 



21 



ber, "show stationary periods where Lehman and Pedersen 
show a decrease," and a continuous rise through the re- 
mainder of the year. 

The resuks from each of the groups of boys are presented 
in the following table. In this table the values for the five 
groups of boys are given in kilograms, for each age sep- 
arately. They are also combined and worked out in per 
cent., the January values being taken as the base, and 



compared with 


Hg 


■ht 


stren 


gth 


and 


with variations in 


temperature. 






















TABLK I 






Date 


Phot. L. 


P. 


J. 


Boys 


Date 


Phot. L. P. J. Boys 


Oct. I 


35-2 38.5 








May 


19 


46.7 40.6 51.5 41.3 32.0 


" II 


36,2 38.2 








Jiin. 


8 


47.8 42.7 50.3 44-8 32.1 


" 21 


337 38.1 








" 


18 


48.6 42.8 50.4 46.3 33.0 


" 31 

Nov. 10 
" 20 


31. J9 Z7a 
31.2 37.9 
28.9 38.2 








July 


28 

8 


45.8 43-3 50.3 45-0 ZZ-I 
46.0 41.9 Si-o 47.2 


" 30 


25.9 37.6 










18 


44.9 42.0 50.5 45-8 


Dec. 10 


25.6 37.0 










23 


49.1 41.6 53.0 43.2 


" 20 


254 2>13 








Aug. 


7 


47.9 41-3 53.3 46.6 


" 30 


26.9 38.7 








" 


17 


45.4 40.1 53.8 46.6 33.0 


Jan. 9 


24.0 37.9 








» 


2.7 


48.1 41.^ 52.7 46.5 ZZ^7 


" 19 


27.8 38.3 








Sept. 


6 


44.8 43-7 52.3 46.1 34.1 


" 29 


28.1 zi.-] 42.4 




26.2 


" 


16 


41.6 46.8 52.5 47-9 33-9 


Feb. 8 


31-5 38.9 


44.2 




27.^ 


" 


26 


41.0 45.3 50.9 49.9 34.3 


" 18 


29.7 381.9 


47.8 




27.8 


Oct. 


6 


37.8 45.!i S3.0 50.8 3K.? 


" 28 

Mh. 10 

" 20 


34.6 39.5 49.1 
35-5 ^9.8 50.7 
36.4 39.2 551.7 




29.2 
29.5 




16 
26 


^.Z 44-8 53-7 49-9 34-3 
30.5 43.7 51.6 49.0 36.4 


" 30 


41.4 40.5 


52.1 


2,1.- 


2 30.5 


Nov. 


5 


29.0 43-7 51-5 48.3 Z7-?> 


Apr. 9 


45.3 41-0 


51.9 


38.: 


7 31.3 


" 


i.S 


32.8 44-1 52.4 487 36.9 


" 19 


37.5 40.5 


53.1 


38.4 30.5 


>> 


25 


:^.o 43.0 52.3 51. 1 37.2 


" 29 


43-4 40.5 


52.6 


42.( 


3 31.4 


Dec. 


5 


29.1 42.5 52.6 51.5 37-0 


May 9 


47.4 40.1 


55.6 


42." 


9 31.8 


" 


T5 


28.3 42.0 52.1 49-2 ZJ--^ 


2C 


) 43.3 42J0 50 


.2 A 


i.i 33. 


I " 


25 


42.0 



The above table shows the weekly averages of Leh- 
man, Pedersen, Miss J., and Group V of the boys when 
compared to changes in the strength of sunlight as recorded 
by a Steenstrup photometer. 



2.2 PE:rI0DIC variations in KFFICIENCY 

TABLE II 
1904 1904 1904 1904 1903 All 



Month 


lO-II 


11-12 


13-14 


12-13 


12-13 


PerC 


Temp. 


Light 


May 


19.6 










IZ.J 


10.2 


45.8 


June 


21.0 


24.2 


27.0 






80.3 


14.5 


47.4 


July 














16.1 


46.7 


Aug. 


22.8 


25.7 


28.6 






86.0 


15.7 


47.1 


Sept. 


22.0 


25.8 


27.9 






84.4 


12.8 


42.5 


Oct. 


25.6 


29.3 


31.8 






95-3 


8.0 


34.3 


Nov. 


26.5 


29.6 


33-9 






100.3 


Z-7 


28.7 


Dec. 


26.6 


29.8 


33.9 






100.7 


0.8 


26.0 


Jan. 


26.6 


29.2 


33-9 


22.7 


25.9 


lOO.O 


— 0.1 


26.6 


Feb. 


27.6 


29.6 


35-2 


23.0 


27.9 


103.6 


0.0 


31.9 


Mch. 


28.2 


31.2 


36.6 


25.6 


29.8 


109.7 


1.2 


37.8 


Apr. 








25.4 


31.0 


115.8 


5-7 


41.7 


May 










32.1 


124.0 


10.2 


45.8 


June 










33.1 


127.7 


14-5 


47-7 


July 














16.1 


46.7 


Aug. 










33.5 


129.3 


15-7 


47.1 


Sept. 










34.1 


131-6 


12.8 


42.5 


Oct. 










35.5 


137.0 


8.0 


35.9 


Nov. 










37-2 


143.5 


Z-l 


30.6 


Dec. 










37.1 


143.2 


0.8 


28.7 



The authors describe the results by saying that muscle 
strength begins to rise in January, with light strength, and 
shows a decided growth through February and March, while 
the temperature is almost constant, and much lower than 
that at which muscle growth stopped in November. It 
still grows in May, when light has attained its maximum, 
but in June and especially in July and August, when heat 
reaches its maximum, growth in muscle strength stops en- 
tirely, and starts again in September, as soon as the heat 
decreases somewhat. The fact of increasing muscle strength 
with falling temperature was noted in both Lehman and 
Pedersen, but in growing persons the growth hides this 
effect. 

The conclusions are as follows : 'The stronger light is, 
the more favorable the actinic rays are to muscle strength. 
Heat has an individually varying and perhaps a movable 



si^ASONAL rj^RioDiciTY IN abii.itie;s 23 

optimum so that both low and high temperatures are de- 
pressing to muscle strength. From the joint influence of 
these two factors there arises the yearly periodical variations 
of muscle strength." 

(5) Criticism. This work is very carefully and sys- 
tematically done. It seems possible, however, that the au- 
thors were a little over-zealous in attempting to explain the 
phonomena of variations in muscle strength as due en- 
tirely to external conditions. As to its aim, means and 
methods of procedure, there is very little to criticise. The 
results, also, are given in detail, so there may be no question 
concerning them. It seems, however, that the authors have 
drawn conclusions not wholly warranted by the facts. 

In the first place, the authors find a "very abrupt rise in 
muscle strength in September." This seems to be a little 
unusual and needs analysis. Of the four sets of records, 
shown in the first table, but one person, Lehman, shows 
such a tendency. Most of the groups of boys in the second 
table show a drop in September, a large rise in October, and 
remain almost stationary until January. This large rise in 
September is a phenomenon which is not found by any other 
investigator, and the fact that there is almost no increase 
in three groups of growing boys during three or four months 
from October to January, would suggest that some unusual 
influence was present, such as a changed adjustment of the 
ergograph or some internal cause. In my own experience, 
I know that merely adjusting a machine or perhaps oiling it, 
makes a great difference in the records. In the presence of 
such a fact, the authors should have studied the records in 
detail for errors and considered such facts in the conclu- 
sions concerning the causes of the variations found. It 
would seem that practice effects plus growth alone would 
show some sort of increase in the abilities of growing boys 
during three or four months. 



24 PERIODIC VARIATIONS IN ^FFlCIElNCY 

In regard to the beneficial effects of light strength and 
heat strength, the authors avoid many seeming contradictions 
in their conclusions by clever explanations. In order to ex- 
plain constant growth in muscle strength they try to find 
some favorable influence for nearly all times of the year, so 
they hit on the combination of light and heat. From Janu- 
ary to May light is beneficial ; from September to November 
normal heat is favorable, while in December decreasing heat 
is unfavorable. When confronted by these seeming contra- 
dictions, they explain them on the basis of a movable opti- 
mum above or below which heat is unfavorable. This is 
perhaps one of the most important ideas in the whole account. 
While there seems to be no doubt about the influence of 
sunlight and especially of changes in temperature on muscle 
strength, it seems to me that many other factors, such as 
food, clothing, and general manner of life should be in- 
cluded as causal factors. Though the authors tried to elim- 
inate these effects as far as possible in the cases of Lehman 
and Pedersen by taking the tests shortly after rising, they 
should not have neglected them entirely. 

Concerning the effects or air pressure, a report of which 
may be found in the section on weather effects, the facts 
seem to be very well established. Here, as in the case of 
temperature, they suggest the theory of an individual opti- 
mum, above or below which atmospheric pressure is injur- 
ious to muscle strength. This question of an individual 
optimum for both air pressure and temperature is very im- 
portant, and should be further investigated. As to the men- 
tal tests, also reported under weather effects, we will pass 
them without criticism as the authors make no positive claim 
for their data. Their remarks on the methods of studying 
mental abilities and on showing the results graphically, are 
well and carefully thought out, and are well worth study. 

All through the article the authors are very sane in their 
treatment of results, and their explanation of the usefulness 



SEASONAI. PERIODICITY IK ABIT.ITIKS 2$ 

of the formulas used in statistical studies is ver}^ valuable. 
On the whole, it is the most scholarly work on periodicity 
which I have found, and must be taken into account by any 
who engage in a similar study. 

5. Seasonal Variations in Diurnal Periodicity. 

(KUHNES) 
(i) Method. Kuhnes made a very thorough investiga- 
tion of diurnal periodicity in physical strength while a 
student at New York University, the results of which I 
have taken from an unpublished thesis. In these tests the 
Smedley Dynamometer was used. The tests, which were 
made mostly on himself, were taken seven times daily for 
505 consecutive days. At each of the seven test periods, the 
average of three records for each hand was taken, the six 
tests being taken in three different positions, first with the 
left, then with the right as follows : 

I — each hand hanging downward. 

2 — each hand held vertically 

3 — each hand held horizontally. 

(2) Results. The principal results are given in the sec- 
tion on Diurnal Periodicity, but there are several state- 
ments in his "Summary and Conclusions" which are of 
value here. They are as follows : 

I — The average diurnal course of efficiency is also the 
course of 88 per cent, of the days. 

2 — There is a distinct seasonal periodicity characterized 
by a maximum in December, a gradual decline through the 
winter with a minimum in February and March, a gradual 
rise during the spring, and a slightly higher one in autumn. 
There are marked fluctuations at the beginning of the spring 
and winter seasons. 

3 — There is a tendency of the curve of efficiency of one 
year to follow the general trend of the curve for the pre- 
ceding year. 

(3) Criticism. The work of Dr. Kuhnes was done in a 



26 PERIODIC VARIATIONS IN EFFICIENCY 

very careful and painstaking maner. The method of eheck^ 
ing was such as to eliminate all accidental or unusual gripsj 
the average of forty-two grips being taken each day, ( twen- 
ty-one with each hand), and the method and procedure were 
strictly uniform and well adapted for the purpose. The fact 
that only one person was tested, a young man of scholarly 
habits not physically strong but in good health, narrows the 
value of the results somewhat, but this is largely outweighed 
by the care and fidelity of the person taking the tests. The 
results from one test person carefully gathered are often of 
far more value than the results from a large number super- 
ficially tested. Next to the investigation of Lehman and 
Pedersen, this is perhaps the most important investigation 
which has yet been made. 

6. Summary of the Main Problems of Seasonae 
Periodicity. 

At this point it may be well to summarize the main prob- 
lems and results of previous investigations of periodicity in 
mental and physical abilities, in order that they may help us 
to a birds-eye view of the problems to be solved. In this 
field we find a great diversity of opinion. There seems to be 
little doubt about the existence of seasonal rhythms in 
growth in height and weight, in blood pressure, and in 
haemoglobin content of the blood, as well as in muscle 
strength and in mental abilities. Though several investiga- 
tors have studied the various aspects of the problem under a 
great variety of conditions and by a great variety of methods, 
the actual course of seasonal periodicity, its chief character- 
istics, and its most noticeable effects are still under discus- 
sion, and the knowledge of its causes is still far from satis- 
factory or complete. 

In physical strength, Schuyten found for growing chil- 
dren a falling period from January to March, a rising period 
from May to June, a falling period from July to September, 
and a rising period from September to December. Lehman 



SEiA^ONAt PERIODICITY IN AfilLlTlE^^ ^') 

and Pedersen found, for a group of growing boys and d 
young girl, a rising period from February to June, a sta- 
tionary period from July to September, and a rise to Decem- 
ber^ with a stationary period from December to February. 
For adults, Lehman and Pedersen found a falling period 
from November to January, a rising period from February 
to June, a falling period from June to August, and a sharp 
rise in September, with a continued rise till November. 

Kuhnes found a maximum in November and December, 
a minimum in Feburary and March, a gradual rise through 
the spring and a slightly higher one in autumn. 

These studies seem to show that the rhythms found for 
adults by Lehman and Pedersen and Kuhnes differ from 
those found for growing young people by Lehman and Pe- 
dersen, and by Schuyten, the curve for young people show- 
ing a stationary period where that for adults shows a de- 
crease. The rhythm for adults seems to show variations a 
short time before that for young people and children. 

In the mental tests, Schuyten found a crest in January, 
with a decrease to July, and an increase from October to 
January. Lobsien found a high level for primary memory 
around January, a low level for February and April, and a 
low level around October, with a rise to January. Lehman 
and Pedersen found the best results in a memory study, 
made on a group of children, in January, and in May, with 
a slight drop in February, June, and September. Many of 
these authors found more or less agreement between mental 
and physical abilities, and weather conditions. Lehman and 
Pedersen go so far as to say that the seasonal variations 
found by them are a direct result of the continued effects of 
temperature and the strength of sunlight. Other authors 
simply find that mental and physical abilities are more or less 
influenced by the weather. With these points in mind, we 
will proceed to the analysis of our original data on seasonal 
periodicity. 



CHAPTER III. 

An original experimental study in sea- 
sonal PERIODICITY 

I. Introduction. During the school year from October, 
1910, to June, 191 1, the writer conducted an original experi- 
mental investigation concerning periodicity as shown in 
mental and physical tests. These tests were made on two 
groups of students in the first year of the Manual Training 
High School of Washington University, St. Louis, Mo. 
The tests were all made under the personal direction of the 
writer at hours ranging from 9 a. m. to 3 p. m., at a time 
when the classes came to his room for a study period. Many 
students took the tests for a part of the time, but only ten 
(referred to as the B. Division) took the tests daily 
throughout the entire period. Another group of twenty-two 
(referred to as the A. Division) took the tests once each 
week on Friday. 

Owing to the amount of time consumed by these tests, it 
was not possible to give more than one physical and one 
mental test daily. The complete record of each of these tests 
will first be described separately, after which the results will 
be compared with one another, and with the results of other 
investigators of periodicity. 

2. Periodicity as Shown in Physical Tests. 

(i) Purpose. The main purpose of these tests was to 
discover any periodic variajtions in musicle strength as 
shown by dynamometric tests in the course of a school year. 
A secondary purpose was to find, if possible, a verification of 
the work of Schuyten, Lobsien, Kuhnes, and Lehman and 
Pedersen. 

(2) Method. As a basis for this investigation a series 
of tests was made for strength of grip, using the Smedley 

28 



ORIGINAL e:xpe:rime:ntai, study 29 

Dynamometer. The tests were made daily on ten boys, and 
weekly on one man of 26 years of age and on twenty-one 
boys, all of the boys being between 13 and 19 years of age. 
They were made at varying times during the day between 
9 a. m. and 3 p. m., except that none were made between 
12 m. and I p. m. All records were made under my personal 
direction, and I was as careful as possible to keep the condi- 
tions uniform throughout the investigation. 

(3) Preliminary Tests. In both the A. and B. Divisions, 
a series of preliminary tests was made for three days, during 
which time each subject found the correct adjustment for 
his hand and learned to use his strength to advantage. It 
was found that when the students took the tests always in 
the same order, only two re-adjustments of the dynamometer 
were necessary during the tests in each division. In this 
way the grip length of each subject was accommodated and 
the same adjustment was made each day for each pupil. 

(4) Procedure. In making the tests each pupil was 
instructed to hold the dynamometer at arm's length, with the 
dial face upward. Each subject was allowed three trials, 
taken alternately for each hand, only the highest record for 
each hand being recorded. This allowed an interval of about 
30 seconds between any two records for the same hand, so 
that the hand recovered from the effects of any strain 
before the next grip was taken. The subjects entered into 
the plan with earnestness and every one did his best, so far 
as the writer could discover, to keep the external conditions 
uniform. 

(5) Results. In checking the results, the averages for 
each day and for each week were computed for each group, 
as was also the average of each pupil in the B. Div. for 
each week. When a pupil was absent, it was found neces- 
sary to count him in making up the daily averages, at his 
average made during the other days of the week. If a 
pupil was absent for a full week at a time he was counted 



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r^og 
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in -* 


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1 



ORiGiNAi, i:xpe:rime:ntai, study 



31 



each day at his average for the preceding week. In this 
way the^ absent pupils could not affect the averages, while 
if a pupil whose record was either above or below the class 
average was omitted from the records for one day, his ab- 
sence might affect the class average very decidedly. The 
record of any pupil who was absent for two full weeks at a 
time was excluded in making up the records. 

The monthly averages of both the A. and D. divi- 
sions for grip strength are found in Table IV. They 
show unmistakably the presence of a seasonable rhythm. 
We find a gradual increase in strength of grip for each 
hand from October to January, a slight decrease for each 
hand in February, a small increase in March followed by a 
continuous increase till June when the tests ended. 

The same results may be seen in Table V for weekly 
averages. The variations in the first three weeks are 
due to the fact that several boys in each group gripped 
so hard that they injured their hands. The large initial 
increase is also partially due to practice. We see, how- 
ever, that the period from October to the middle of Jan- 
uary, is favorable . Then comes a period of depression 
until March, and a period of gradual increase until the end 
of the tests in June. 

The same results may be observed in Tables VIII, IX, 
and X, where, with two or three small exceptions, we find 
low records for the month of February for both hands at all 
ages. A nineteen and a twenty-six year old subject both 
agree in showing a practically stationary period from De- 
cember until March instead of a drop in February, otherwise 
they agree with the seasonal rhythm of the younger boys. 
These facts seem to agree with the results of other investi- 
gators on adults in showing a rhythm for adults which dif- 
fers slightly from that of growing children, showing a sta- 
tionary period where the growing children show great flue- 





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05T-H(M 


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Division. 
Apr 
41.3 
38.5 
10.7 


Division. 
56.4 
54.3 
10.8 


Grip. A 

Mch 

40.8 

37. 

10.7 


WcDiXN 


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Dec 
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Table 
52.9 

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10.4 


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ORIGINAL EXPERIMENTAL STUDY 33 

tuations, some showing an increase while others show a de- 
crease. 

3. Periodicity as Shown in Primary Memory Tests. 
(i) Purpose. The main purpose of this investigation 
was to discover any periodic variations in mental abilities as 
shown in primary memory tests, given through a school year. 
A secondary purpose was to see how the variations com- 
pared with those found by other investigators of mental 
periodicity, and how they compared with the results from 
the dynamometric tests given to the same groups of students, 
on the same days, at the same hours, and during the same 
school year. 

(2) Method. As a basis for this investigation, a series 
of tests was made to discover the ability of the two groups 
already referred to as the A. and B. divisions in the dynamo- 
metric tests, to reproduce three series of four, five, and six 
numbers of two digits each, immediately after they were 
read by the author. The tests were given immediately fol- 
lowing the dynamometric tests. The group to be tested was 
seated in front of the investigator. At a given signal all of 
the students were requested to come to attention. 

(3) Procedure. A series of four numbers, as 84-26- 
47-32, was read at the rate of one per second. At the close 
of each series, the students were allowed 15 seconds to write 
the series of numbers in the order of presentation, on a 
record blank provided for the purpose. This blank bore the 
name of the pupil and of the division, the time of day, date, 
character of the day, and the result of the dynamometric 
tests which had just been given. Fifteen seconds after the 
four numbers were written, at a given signal, a series of five 
two place numbers was read at the same rate as before. 
Then after waiting fifteen seconds for the pupils to write the 
series of five numbers on the record blanks, the attention sig- 
nal was given, followed by six two place numbers at the 
same rate as before. After the pupils had written the series 



34 PERIODIC VARIATIONS IN EFFICIENCY 

of six numbers, they were asked to give any facts which 
helped or hindered them in writing the numbers, on the 
reverse side of the record sheet. The time of day, the char- 
acter of the day in general and the temperature were then 
recorded along with any interesting introspections of the 
students, after which the records were collected. In esti- 
mating values, a number correctly given in its proper order 
was counted one point. A number rightly given but in the 
wrong order was counted one-half point. A number which 
had one digit correctly given was also counted half a point. 
The total score that could be made, therefore, was 15 points. 

(4) Preliminary Tests. In this investigation, as in the 
one on muscular periodicity, a series of preliminary tests 
was given on three days. The purpose of the experiment 
was explained to the pupils, who entered into the spirit of 
the investigation with enthusiasm. As in the dynamometric 
tests, no one was asked to take the tests unless he so desired. 
In this experiment, also, absent students were counted at 
their average for the week, or if absent for a whole week, at 
their average for the preceding week. Those who were ab- 
sent for more than two consecutive weeks were dropped from 
the investigation. 

(5) Results. In this investigation, the averages for 
each day, each week, and each month, were computed both 
for the individuals, for all ages, and for each group as a 
whole. 

The monthly variations for primary memory for both 
the A. and B. divisions are shown in Tables III, XI and 
XII. The tables for the B. division show a characteris- 
tic curve similar to the curve for muscular growth, that 
for the A. division does not show the same characteris- 
tics. The only striking similarity is found in the depres- 
sion for February, a depression which is found in all 
the monthly curves for both mental and physical tests. If 
we examine Table XI we find this same depression for all 



ORIGINAI. e:xpi:rIMKNTAIv STUDY 35 

ages in February and March. The same depression is 
found in nearly all ages of the A. group (Table XII), ex- 
cept the two oldest subjects. Here we find the depression in 
January and March instead of February, as with the young- 
er boys. The only other exceptions are two boys, both very 
bright and very nervous, at age 13-14 whose records were 
high through all the year. The high record for the A. 
division in November is due to an exceptionally high aver- 
age of the two boys mentioned, for the month. The high 
record for the A. division for May and June was due largely 
to the individual record of an 1 8-year-old boy. During that 
time this particular boy was under a very high nervous 
tension. He was a part owner of an airdome which opened 
about that time, and he spent his evenings there until nearly 
midnight. He was old for the class but very bright. He 
had been out of school for about four years just preceeding 
this time. His increase in ability was therefore due very 
largely to habit and effects of practice, and was phenomenal. 
He was very thorough and painstaking, and his record shows 
what a year of conscientious study can do in sharpening a 
boy's mental ability. 

With the exception of the two older students noted above, 
the A. division consisted of boys who had been in school 
continuously, and as a whole they showed very little change 
as a result of practice. They were all taking the Latin 
Course. The B. division was almost exactly opposite in com- 
position. They were taking the English Course, and in gen- 
eral were more mature. Only two of the ten had attended 
school continuously. The others had all been at work for at 
least one term since graduation from a grammar school, and 
two had been out of school for three years preceding. In 
the B. division, therefore, we find that the low record for 
October was quite general. Then as a result of practice 
largely, it makes a very noticeable increase during the year, 
reaching a higher level than is reached by the A. division. 



36 PERIODIC VARIATIONS IN e:F^ICIE:NCY 

The very high records for April, May, and June, were due 
to the efforts of two very bright boys, both of whom had been 
out of school during the two years next preceding. The 
rise of these two boys, as well as that for the whole B. divi- 
sion, was due to the same cause as that of the nineteen-year- 
old in the T. division mentioned above — earnest application. 
If we eliminate these special cases and the practice effects, we 
find that the curve for the B. division Memory Tests becomes 
more nearly level, the one outstanding feature being a 
slight drop sometime in January and February. We must 
conclude, therefore, that the curve for primary memory 
shows a rising tendency with favorable influences from 
October to January, a period of depression for January, 
February, and the first part of March, and a rising tendency 
with favorable influences from March to June. 

4. Comparisons of Mijntal and Physical Se:asonal 
Pkriodicity. 

If we compare the results from the mental and physical 
tests in the two accounts just given, they show certain strik- 
ing similarities. They all show a sharp rise at the begin- 
ning, a regular improvement until January, a period of de- 
pression from the middle of January to the first of March, 
and a regular rise to the ends of the tests. While there are 
a few differences, the general tendencies outweigh them. 
The larger changes in muscle strength are undoubtedly due 
to a large extent to physical growth and practice effects. 
In Tables IX and X, we find that the greatest increase in 
physical strength was in boys from 15 to 17 years old. W^ 
also see that the increase for nine months for those who took 
the tests five times per week was for all ages nearly double 
the increase made by those who took the tests but once per 
week. It would seem, therefore, that about one-half of the 
improvement of the B. division was the effect of the extra 
practice received by that group. 



ORlGINAIv e:XPE:RIMI:NTAIv STUDY 5/ 

We also have the interesting phenomena that at all ages 
except at 16-17, the gain with the left hand was greater than 
with the right, in one case being three times as great. The 
average gains with the right and left hands for those who 
took the tests five times weekly was 12.7 Kg. and 14.5 Kg., 
respectively, while that for those tested but once per week 
was 6.2 Kg. and 7.2 Kg., respectively, for the same time. In 
no case was a continuous gain made during each of the nine 
months except in the case of one boy 15-16 years old in the 
B. division. 

In the Mental Tests the efifects of practice and growth 
are very small. In no case in either group was a continuous 
monthly gain made throughout the year. With the exception 
of five individuals, every boy had made his highest record 
of the entire series of tests by the first of January. The 
highest records in the entire set of tests were made by five 
individuals, two of the very bright boys between the ages of 
13 and 14 years, and three older boys, one 17, one 18, and 
one 19 years old, each of whom had been out of school and 
working during the two or three years just preceding. 

The Dynamometric tests for variations in physical abili- 
ties seem to be an excellent means for judging the growth 
and development of physical strength. The same validity, 
however, cannot be claimed for the mental tests used in this 
investigation. Records made by individuals from day to day 
were very erratic, and often seemed to be without any ap- 
parent causes in spite of all precautions to make the material 
and procedure uniform from day to day. 

The abilities of this group in primary memory were prac- 
tically fixed before the tests began, and in only a few cases 
were any large practice effects noticeable. One of the great- 
est difficulties in mental tests is that many boys become con- 
fused when engaged in taking them. Among the ten boys 
in the B. division who took the tests daily, five could 
usually be depended upon to make good scores. The other 



38 PKRIODIC VARIATIONS IN I^I^FICIENCY 

five were very nervous and easily became confused, making 
often very low records. I have taken the individual records 
of each boy, and by comparing them with the records of tem- 
perature, humidity, etc., sought to discover causes. In most 
cases the results of such comparisons are contradictory or 
baffling. But this is a condition that every one who gives 
mental tests must expect to meet, and in order to meet it, the 
investigators depend on statistics. 

Every science grows by improvement in its methods, and 
while the method used in the mental tests is far from perfect, 
it is about as reliable as any yet devised. The memory re- 
sults are valuable because this is one of the most exhaustive 
tests ever made, and they are doubly valuable for purposes of 
comparison with the records of the physical tests, given to 
the same groups at the same time each day for so long a 
period. So far as I have been able to discover, it is the only 
investigation which combines the results of mental and 
physical tests on a homogeneous group for so long a time. 

A comparison of the tables shows quite conclusively 
that the same set of causes operate, to a certain extent 
at least, in controlling both mental and physical abilities 
through a relationship as yet unknown in detail. This 
is especially seen in the period of depression in January and 
February, a period which all investigators have found, 
though the exact time it occurs differs in individuals, and in 
all probability differs under varying weather conditions. The 
school building where the boys spent their time was almost 
ideal as to light, space, ventilation, temperature, and humid- 
ity, and these favorable surroundings tended to cause both 
mental and physical energy to grow beyond the time where 
a pause usually takes place. 

The individual records show that the period of depression 
in muscle strength begins anywhere between the middle of 
December and the middle of January, and lasts from 3 to 
10 weeks. In some subjects its effects are overcome by the 



ORIGlNAIv E:XPKRlMi:NTAt STUDY 39 

middle of February, in others it lasts until sometime in 
March, and in one case of a 17-year-old boy, it lasted from 
February to May. In general the boys of low vitality in 
the early winter, are the ones who show the depression first. 
Several boys showed more than one period of depression, but 
the only period of depression shown by every individual 
tested was the one which began some time between the mid- 
dle of December and the middle of January, and lasted from 
three to ten weeks, varying with individuals. 

While the averages for the memory tests show the same 
general tendencies, the depression tends to appear slightly 
earlier in some cases and slightly later in others. The rec- 
ords from day to day vary so much, due to accidental causes, 
that it is sometimes difficult to see the depressions in the 
weekly averages, but the individual monthly averages bring 
out the depression referred to in the preceeding sentence in 
almost every individual tested. 

These results tend to confirm the results of Kuhnes and 
Lehman and Pedersen on one hand, and those of Schuyten 
and Lehman and Pedersen on the other. They show that in 
periodicity, the time and extent of the period of depression 
about the beginning of the year is different for adults and 
for youths. They also tend to clear up the conflicting results 
of other investigators who found periods of depression all the 
way from November to March, by showing that these are 
simply individual variations of a more or less universal 
phenomenon. 

They tend to dispute the idea that physical and mental 
abilities go by contraries as do growth in height and weight. 
Finally, they give added validity to the idea of a seasonal 
growth rhythm, a cosmic rhythm, which, allowing for various 
individual differences in adaptation, affects all individuals 
profoundly, and is manifested in a multitude of ways in 
human life. 



40 



TABIvK VIII 



Table VIII, 


B Division 




Weekly Av 


Erag: 


es 








Hu- 


% 


Char. 




















Avg. 


mid-Suu 


of 


















Mo. Tern. 


ity shine 


dav 


Hf 


T r 


R 


L 


M 


4's 


5's 


6'? 


Oct. 10 


58 


-93 


100 


CI 


2 


P.M. 


43 


40 


10.3 


4 


3.1 


3.2 


11 


64 


91 


60 


CI 


10 


A. 


43.3 


39.5 


8.3 


3.3 


2.5 


2.5 


12 


67 


91 


77 


CI 


11 


A. 


46.1 


41 


8.2 


3.1 


2.8 


!2;.3 


13 


68 


57 


58 


Pc 


1 


P. 


46.2 


42.9 


11 


3.7 


4.1 


3.2 


14 


70 


69 


60 


Pc. 


1 


P. 


44.7 


.42.4 


10.5 


4 


3.5 


3 


17 


74 


53 


87 


CI 


2. 


P. 


44.9 


42 


8.8 


3.3 


3.1 


2.4 


18 


74 


82 


100 


CI 


11 


A. 


46.2 


41.3 


9 


2.8 


3.2 


3 


19 


65 


80 


76 


CI 


1 


P. 


45.9 


43.3 


9.4 


3.4 


3.5 


2.5 


20 


47 


86 





c 


9 


A. 


43.7 


42.3 


9.8 


3.4 


3.4 


3 


21 


44 


94 





c 


1 


P. 


42.6 


43 


9.4 


3.5 


3.1 


3.5 


24 


60 


51 


©9 


Cl 


9 


A. 


45.5 


42.4 


10 


3.7 


2.9 


3.4 


25 


58 


24 


81 


CI 


1 P. 


50.5 


44.3 


9.3 


3.2 


3.4 


2.7 


26 


67 


64 


90 


Cl 


9 


A. 


47.2 


45.3 


9.5 


2.5 


3.8 


3.2 


27 


46 


36 


56 


Pc 


1 


P. 


47.7 


43.9 


9 


3.8 


2.3 


2.9 


28 


34 


55 





c 


1 


P. 


49.6 


42.5 


8.8 


3.5 


2.6 


2.7 


31 


59 


44 


75 


Cl 


10 


A. 


49.6 


44 


11.7 


3.8 


4.3 


3.6 


Nov. 1 


54 


68 


12 


c 


1 


P. 


48.7 


47.4 


10.5 


3.6 


3.3 


3.6 


2 


40 


63 


79 


Cl 


9 


A. 


47.9 


43.5 


10.3 


3.'9 


3.3 


3.1 


3 


36 


56 


100 


Cl 


9 


A. 


47.8 


44.2 


9.7 


3.2 


3.3 


3.2 


4 


38 


63 





c 


9 


A. 


46.6 


43.7 


10.8 


4 


3.5 


3.3 


7 


54 


65 


100 


Cl 


9 


A. 


49.2 


45.9 


10.1 


3.5 


3.7 


2.9 


8 


51 


80 


87 


Cl 


10 


A. 


48.1 


45.5 


11.6 


3.9 


4.2 


3.5 


9 


60 


73 


91 


Cl 


9 


A. 


50.1 


46.3 


10.9 


3.8 


3 


4.1 


10 


40 


87 


59 


Pc 


9 


A. 


49.6 


44.8 


9.9 


3.8 


3.2 


2.9 


11 


36 


77 


98 


Cl 


9 


A. 


49 


46.6 


10 


3.8 


3.1 


3.1 


14 


40 


54 


49 


c 


2 


P. 


51.2 


46.1 


11 


3.3 


3.3 


4.4 


15 


34 


69 





c 


2 


P. 


49.3 


44.7 


11.3 


3.8 


3.8 


3.7 


16 


34 


85 


46 


Pc 


2 


P. 


50.7 


47.5 


10.7 


4 


3.1 


3.6 


17 


33 


70 


'0 


c 


2 


P. 


50.5 


47.3 


10.9 


3.6 


3.6 


3.7 


18 


40 


60 


20 


C 


2 


P. 


49 


47.9 


9.5 


3.5 


2.9 


3.1 


21 


44 


72 


7 


Pc 


2 


P. 


50.1 


48.4 


10.2 


3.3 


3.3 


3.6 


22 


40 


87 


100 


Cl 


1 


P. 


50 


47.9 


11.6 


3.9 


3.8 


3.9 


23 


52 


61 


100 


Cl 


11 


A. 


51.4 


49.4 


9.2 


3.7 


2.8 


2.7 


24 










Thanksg 


;iving Day 










25 


49 


49 


82 


Cl 


2 


P. 


51.2 


48.1 


10.4 


3.7 


3.3 


3.4 


28 


32 


72 


95 


Cl 


2 


P. 


52.6 


48.6 


8.9 


3.6 


2.8 


2.5 


29 


32 


84 


8 


Pc 


2 


P. 


51.8 


48.1 


10.7 


3.8 


3.5 


3.4 


30 


26 


5'9 


100 


Cl 


11 


A. 


52.2 


49.4 


10.9 


3.8 


3.3 


3.8 


Dec. 1 


23 


64 





c 


2 


P. 


53 


49.4 


9.9 


3 


3.4 


3.5 


2 


26 


52 


23 


c 


2 


P. 


52 


50.1 


11 


3.9 


3.1 


4 


5 


30 


61 





c 


2 


P. 


52.1 


49.5 


10.7 


3.5 


3.8 


3.4 


6 


26 


49 





c 


1 


P. 


53.5 


49.3 


10.9 


3.8 


4 


3.1 


7 


28 


60 


76 


Cl 


2 


P. 


50.3 


48.7 


10.2 


3.3 


3 


3.9 


8 


30 


50 


39 


Cl 


1 


P. 


52.1 


49.4 


9.2 


3.4 


2.7 


3.1 


9 


34 


64 


4 


c 


2 


P. 


51.3 


48.5 


1'0.8 


3.6 


3.4 


3.8 



TABLK VIII (Con'd) 



41 



Tabi^e: VIII, B Division 

Hu- 9f Char. 
Avg. mid-Sun of 



Weeki^y Ave:rage:s 



Mo. 


Tem, 


. itys 


shine 


day 


Hour 


R 


L 


M 


4's 


5'.s 


6's 


12 


21 


52 


33 


Pc 


2 P. 


54.9 


53.6 


11.1 


4 


3.2 


3.9 


13 


21 


50 


70 


CI 


2 P. 


52.4 


46.7 


11 


3.6 


3.7 


3.7 


14 


34 


30 


100 


CI 


2 P. 


51.7 


49.2 


11.2 


3.3 


3.7 


4.2 


15 


38 


51 


84 


CI 


2 P. 


51.4 


49.6 


9.7 


3.9 


2.8 


3 


16 


36 


58 


100 


CI 


2 P. 


52.3 


47.7 


10.3 


3.8 


3.2 


3.3 


19 


39 


48 


38 


c 


2 P. 


53.4 


48.9 


11.6 


3.6 


3.7 


4.3 


20 


28 


69 


79 


CI 


10 A. 


54.3 


49.9 


11.2 


3.6 


3.6 


4 


21 


30 


59 


69 


Cl 


1 P. 


52.8 


49.8 


11.1 


3.5 


4.6 


3 


22 


36 


95 





c 


2 P. 


52.9 


50.3 


11.5 


3.8 


3.9 


3.8 


23 


30 


62 


66 


Cl 


1 P. 


55.3 


51 


11.9 


4 


4.2 


3.7 


Jan. 9 


32 


47 


83 


Cl 


2 P. 


53.6 


51.2 


12.1 


3.6 


3.9 


4.6 


10 


46 


69 


92 


Pc 


2 P. 


53.8 


52.1 


10 


3.6 


3 


3.4 


11 


51 


81 


38 


c 


2 P. 


54 


51.2 


9.9 


3.5 


3.5 


2.9 


12 


30 


83 





c 


2 P. 


54.5 


50.5 


10.3 


3.7 


3.6 


3 


13 


36 


100 





c 


2 P. 


53.8 


50.9 


10.5 


3.7 


3.6 


3.2 


16 


25 


72 





c 


2 P. 


53.9 


52.4 


10.4 


3.8 


3.6 


3 


17 


27 


100 





c 


2 P. 


55.5 


51 


10.6 


3.7 


3.4 


3.5 


18 


26 


93 





c 


2 P. 


55 


52.5 


11.4 


3.8 


3.7 


3.9 


19 


37 


96 


85 


Cl 


2 P. 


55 


50.2 


10.5 


3.5 


3.5 


3.5 


20 


44 


87 


6 


C 


2 P. 


55.8 


52.2 


11.6 


3.3 


3.6 


4.7 


23 


34 


61 


68 


Pc 


2 P. 


52.9 


49 


9.8 


3.8 


3.1 


2.9 


24 


40 


60 


49 


c 


2 P. 


54.5 


51.7 


10.4 


4 


2.5 


3.9 


25 


47 


88 





C 


2 P. 


54.9 


52.4 


10.9 


4 


3.5 


3.4 


26 


58 


76 


44 


c 


2 P. 


53.9 


51.5 


10.5 


3.9 


3.6 


3 


27 


49 


84 


9 


C 


2 P. 


55.9 


52.2 


10.8 


4 


3.9 


2.9 


30 


34 


55 


76 


Cl 


2 P. 


53.3 


50.7 


10.7 


4 


2.9 


3.8 


31 


48 


66 


73 


Pc 


2 P. 


53.8 


50.9 


10.2 


3.9 


3.2 


3.1 


Feb. 1 


64 


44 


100 


Cl 


2 P. 


54.6 


49.9 


11.2 


3.8 


3.5 


3.9 


2 


36 


73 


100 


Cl 


2 P. 


53.9 


50.5 


10.8 


3.2 


3.2 


4.4 


3 


36 


81 


16 


C 


.2 P- 


53.9 


50.5 


11 


4 


3.5 


3.5 


6 


35 


89 





c 


2 P. 


54.1 


49.8 


10 


3.1 


3.2 


3.7 


7 


34 


82 


2 


c 


2 P. 


53.5 


49.9 


10.2 


3.4 


3.2 


3.6 


8 


33 


67 


73 


Pc 


2 P. 


54.1 


51.3 


10.2 


3.2 


3.5 


3.5 


9 


35 


78 : 


100 


Cl 


2 P. 


54.3 


50.4 


9.8 


3.3 


3.1 


3.4 


10 


30 


64 : 


100 


Cl 


2 P. 


54.4 


51.8 


10.1 


3.6 


3.4 


3.1 


13 


48 


90 


38 


c 


2 P. 


53.5 


50.8 


9.5 


3.4 


3.3 


2.8 


14 


50 


67 


54 


Ps 


2 P. 


54.7 


49.9 


9.5 


3.1 


2.7 


3.7 


15 


54 


48 : 


100 


Cl 


2 P. 


55.3 


51 


9.6 


3.6 


3.5 


2.5 


16 


66 


77 


45 


Pc 


2 P. 


55.3 


52.5 


10.7 


3.7 


3.7 


3.3 


17 


60 


82 


89 


Cl 


2 P. 


54.9 


52.3 


9.7 


3.4 


3.3 


3 


20 


23 


76 


42 


Pc 


2 P. 


54.5 


51.5 


10 


4 


3.1 


2.9 


21 


20 


83 


75 


Pc 


2 P. 


54.7 


51.5 


9.8 


3.9 


2.5 


3.4 


22 










Washin 


^ton"s Birthday 








23 


30 


89 


61 


Cl 


2 P. 


53.3 


52.3 


10.8 


4 


3.6 


3.2 


24 


36 


80 100 


CI 


2 P. 


53.7 


53.1 


9.2 


3.1 


3.1 


3 



42 



TABLK VIII (Con't) 



Table: viii, B Division 

Hu- % Char. 
Avgi. mid-Sun of 



Wkekly Ave:rage:s 



Mo. Tern. 


ity s 


ihine 


day 


Ho'u- 


R 


L 


M 


4's 


5'.s 


6's 


27 


34 


77 


100 


CI 


2 P. 


53.9 


51.2 


9.8 


3.5 


3.3 


3 


28 


28 


100 





C 


2 P. 


53.3 


51.4 


10.1 


3.4 


3.6 


3.1 


Mch. 1 


310' 


75 


25 


C 


2 P. 


52.5 


51.4 


10.3 


3.1 


3.2 


3.3 


2 


36 


84 


100 


CI 


2 P. 


53 


51.3 


10.2 


3.4 


3.2 


3.6 


3 


49 


68 


100 


01 


2 P. 


55 


52.8 


10.1 


3.9 


3 


3.2 


6 


52 


74 


32 


Pc 


2 P. 


54.4 


51.9 


10.2 


3.8 


3.1 


3.3 


7 


43 


79 





C 


2 P. 


54.3 


52.7 


10.9 


3.6 


3 


4.3 


s 


48 


59 


66 


CI 


2 P. 


55 


52.5 


9.2 


4 


2.4 


2.8 


9 


60 


59 


79 


CI 


2 P. 


55.1 


52.3 


9.8 


3.7 


2.9 


3.2 


10 


56 


42 


52 


Pc 


2 P. 


54.9 


52.9 


11 


3.7 


3.3 


4 


13 


40 


48 


90 


CI 


2 P. 


54.3 


52.3 


11 


3.9 


3.6 


3.5 


14 


46 


31 


'97 


CI 


2 P. 


54.4 


52.5 


10.8 


3.9 


3.4 


3.5 


15 


36 


51 


96 


CI 


2 P. 


54.5 


53 


10.5 


3.4 


2.8 


4.3 


16 


30 


36 


85 


Pc 


2 P. 


55.7 


54.1 


10.6 


3.9 


3.3 


3.4 


17 


50 


97 


39 


Pc 


2 P. 


55.1 


52.9 


'9.1 


3 


3.7 


2.4 


20 


59 


27 


100 


CI 


2 P. 


56.3 


53.3 


10.4 


3.7 


3.1 


3.6 


21 


64 


32 


84 


CI 


2 P. 


54.3 


53.5 


11.8 


4 


3.8 


4 


22 


54 


28 


67 


C 


2 P. 


54.9 


53.5 


10.9 


3.8 


2.9 


4.2 


23 


42 


39 


100 


CI • 


2 P. 


55.4 


52.9 


12 


3.9 


3.9 


4.2 


24 


43 


32 


100 


CI 


2 P. 


53.8 


51.4 


10.7 


3.7 


3.3 


3.7 


27 


41 


42 


90 


CI 


2 P. 


55.5 


52.8 


11.6 


4 


3.9 


3.7 


28 


50 


36 


81 


CI 


2 P. 


55.3 


53.4 


10.1 


3.3 


2.8 


4 


29 


45 


84 


58 


Pc 


2 P. 


55.8 


53.5 


10 


3.8 


3 


3.2 


30 


37 


45 


59 


Pc 


2 P. 


54.9 


54 


9.7 


3 


3.1 


3.6 


31 


38 


52 


6 


CI 


2 P. 


55.2 


52.7 


11.0 


3.8 


3.8 


3.4 


Apr. 3 


44 


91 


4 


CI 


2 P. 


54.6 


53.8 


11.5 


3.8 


3.6 


4.1 


4 


58 


81 


30 


CI 


2 P. 


54.6 


54.6 


12.2 


3.6 


3.9 


4.7 


5 


48 


63 


29 


CI 


2 P. 


56.2 


53.2 


10.5 


3.5 


3 


4 


6 


58 


77 


47 


CI 


2 P. 


56.1 


54.8 


11.2 


4 


4 


3.2 


7 


39 


50 


29 


CI 


2 P. 


56.2 


53.2 


10.9 


4 


3.4 


3.5 


10 


50 


44 


75 


Pc 


2 P. 


55.7 


55.1 


11.8 


3.8 


4.3 


3.7 


11 


52 


93 





C 


2 P. 


56.7 


53.9 


9.8 


2.9 


3 


3.9 


12 


60 


61 


63 


Pc 


2 P. 


55.8 


53.6 


11.1 


3.7 


3.2 


4.2 


13 


60 


94 


34 


C 


2 P. 


55.9 


54 


11.5 


3.9 


3.6 


4 


14 


4'9 


44 


73 


CI 


2 P. 


55.9 


54 


11.5 


3.8 


3.5 


4.2 


17 


64 


30 


84 


CI 


2 P. 


54.4 


52.2 


11.7 


3.6 


3.9 


4.2 


18 


59 


86 


7 


C 


2 P. 


57.8 


55.3 


10.0 


3.3 


3 


3.7 


19 


58 


60 


61 


Pc 


2 P. 


57.8 


54.5 


9.7 


3.3 


3 


3.4 


20 


60 


50 


50 


Pc 


2 P. 


56.8 


54.1 


10.7 


3.5 


3.4 


3.8 


21 


60 


37 


74 


CI 


2 P. 


56 


54.1 


10.3 


3.4 


3.2 


3.7 


24 


50 


43 


99 


CI 


2 P. 


56.3 


53.5 


10.4 


3.7 


3.1 


3.6 


25 


54 


38 


100 


CI 


2 P. 


56.4 


55 


12.7 


4 


3.7 


5 


26 


62 


36 


67 


Pc 


2 P. 


56.4 


55.8 


11.7 


4 


2.7 


5 


27 


56 


83 


0' 


C 


2 P. 


58.9 


55.8 


10.2 


3.7 


3 


3.5 


28 


64 


66 


31 


PC 


3 p. 


57 


54.8 


11.2. 


3.8 


3.1 


4.3 



TABI.E: VIII (Coil'd) 



43 



Table: viii, B Division 

Hu- o/^ Char. 
Avg. mid-Sun of 



W^KKLY Averages 



Mo. ' 


Tern. 


itv shine ( 


dav 


TT- 




R 


J. 


M 


4"-^ 


.5's 


6'P 


May 1 


51 


96 


3 


C 


2 


P. 


57 


54.3 


12.3 


4 


3.9 


4.4 


2 


48 


42 


100 


CI 


2 


P. 


57.7 


53.7 


11.9 


3.4 


3.9 


4.6 


3 


49 


40 


7 


c 


2 


P. 


58.9 


57.3 


10.8 


4 


3.5 


3.3 


4 


54 


35 


100 


CI 


2P. 


59.2 


54.3 


11.2 


3.9 


3.4 


4.9 


5 


55 


32 


100 


CI 


2 


P. 


58.7 


55.8 


11.5 


3.7 


3.7 


4.1 


8 


71 


50 


100 


CI 


2 


P. 


57.1 


55.4 


10.9 


3.9 


3.1 


3.9 


9 


78 


35 


99 


CI 


2P. 


59.0 


55.9 


11.7 


3.3 


4.4 


3.9 


10 


76 


47 


100 


CI 


2 


P. 


58.6 


54.6 


10.5 


3.7 


3.8 


3 


11 


70 


36 


80 


PC 


2 


P. 


59.7 


55.6 


11.0 


3.8 


4.1 


3.1 


12 


72 


27 


89 


PC 


2 


P. 


58.6 


55.4 


11.1 


3.7 


4 


3.4 


15 


76 


43 


92 


CI 


2 


P. 


60.1 


56.8 


10.8 


3.9 


3.8 


3.1 


16 


78 


52 


78 


Ol 


2 


P. 


59.9 


54.5 


10.6 


3.7 


3.5 


3.4 


17 


80 


53 


100 


01 


2 


P. 


58.7 


53.6 


10.5 


3.7 


3.3 


3.5 


18 


81 


47 


90 


CI 


2 


P. 


58.4 


55.1 


11.6 


3.5 


3.8 


4.3 


19 


78 


53 


100 


CI 


2 


P. 


58.4 


54.3 


11.5 


3.9 


4 


3.6 


22 


71 


40 


86 


CI 


2 


P. 


58.9 


55 


11.3 


4 


4 


3.3 


23 


70 


37 


100 


CI 


2 


P. 


59.5 


55.4 


11.5 


3.9 


3.8 


3.3 


24 


78 


29 


100 


CI 


2 


P. 


59.8 


55.6 


11.2 


3.2 


3.9 


4.1 


25 


82 


38 


lOO 


CI 


2 


P. 


58.4 


56 


11.1 


3.5 


4.2 


3.4 


26 


83 


41 


98 


CI 


2 


P. 


57.8 


54.6 


11.4 


3.6 


4.1 


3.7 


29 


77 


53 


84 


CI 


2 


P. 


58.6 


56.4 


10.5 


3.5 


3.6 


3.4 


30 


78 


67 


82 


Pc 


2 


P. 


59.6 


57.8 


11 


3.8 


4.1 


3.1 


31 


74 


53 


78 


CI 


2 


P. 


59 


57.7 


11.2 


3.6 


4 


3.6 


June 1 


72 


54 


87 


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2 


P. 


59.3 


57.7 


11.3 


3.7 


3.8 


3.8 


2 


76 


49 


82 


Pc 


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P. 


59.7 


57.3 


11 


3.5 


3.9 


3.6 







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CHAPTE:r IV. 

DIURNAL VARIATIONS IN EFFICIENCY 

I. Introduction. The question of diurnal variations in 
mental and physical abilities has received a great deal of at- 
tention during the past few years, and since it is involved 
in the larger question of seasonal periodicity, a brief survey 
of the progress in this field will be presented and the results 
of others compared with those of my own original investiga- 
tions. The results in this field show, with minor differences, 
a substantial agreement. Several years ago, Lombard^^, 
in a series of experiments using his modification of Mosso's 
Ergograph, found the most favorable periods of the day to be 
between lo and ii a. m. and lo and up. m., and the poorest 
between 3 and 4 a. m. and 3 and 4 p. m. He also noted a rise 
in ability about 2 p. m., which entirely disappeared between 
3 and 4 p. m. 

Patrice^^, in testing the strength of himslf and one other 
with Mosso's Ergograph, found 2 130 p. m. to be the best 
period, the evening to be superior to the morning and to the 
midnight periods, which were about equal. 

Harley^^ gives the following as the results of a six-day 
Ergographic test: 

Hour 9 10 II 12 I 2 3 4 5 6 7 8 

K-M 6.2 6.4 8.7 7.0 9.5 8.2 9.9 7.8 8.9 8.7 7.2 8.8 

This shows a steady rise till 11 a. m., a slight fall at noon, a 
rise at i p. m., another slight drop at 2 p. m. with a crest 
at 3 p. m. This is followed by an irregular decline through 
the rest of the test period. 

Krsepelin^o found a rather unusual variation consisting of 
a gradually increasing efficiency during the three or four 
hours after each meal. He explains this decrease of muscular 

48 



DIURNAIv VARIATIONS 49 

ability as the result of the increased demands on the blood 
supply during the process of digestion. At least one German 
investigator, Roemer, has reported similar variations. 

Christopher^, in a series of 90 second Ergographic tests, 
on 1127 Chicago school children at each hour of the day, to- 
gether with more extended tests with four boys and four 
girls, finds a maximum at 9 a. m., a slight decrease till 1 1 130 
a. m., where there is a heavy loss, and this is followed by a 
renewal of energy at i p. m., increasing to the highest point 
at 2:30 p. m., whence it descends till 4 p. m. His results 
show ( I ) that there is a much greater drop in efficiency dur- 
ing the morning period than in the afternoon, and that (2) 
strength is not so great in the afternoon as in the morning, 
but it is better sustained. 

2. Daily Variations in Voluntary Muscle Contrac- 
tions. (Storey) 37 

(i) Method. During the year 1899, Storey, then at 
Stanford University, tested a number of individuals at irre- 
gular intervals, as to the daily variations in the power of 
voluntary muscular contraction. In the first tests, Lombard's 
modifications of Mosso's Ergograph was used. Later he 
used the Upham Dynamometer. 

(2) Results. He found a rise in power each morning 
till 10 or II a. m., a fall till i p. m., a rise till 4 p. m., and a 
fall till 6 p. m. The morning maximum comes near 1 1 a. m. 
and the afternoon maximum comes near 4 p. m. 

(3) Conclusions. The following is a summary of his 
more important conclusions : 

I — Mental or muscular work producing partial fatigue, 
i. e., not exhaustion, reduces the power of voluntary 
muscular contraction. 

2 — Sleep and food restore ability to work. 

3 — The power of voluntary muscular contraction is 
directly influenced by bodily health. 



50 PERIODIC VARIATIONS IN e:F1?ICIE:NCY 

4 — Exercise has an immediate and stimulating effect on 

the power of muscular contraction. 
5 — Ordinary variations in temperature have no percep- 
tible effect. 

(4) Criticism. This was a pioneer in the field, and like 
all pioneer investigations, the method and procedure are, 
perhaps, not so carefully controlled as they might be. Many 
details are lacking in the report, and the details are poorly 
presented. As a pioneer work, his investigations are worthy 
of mention. 

3. The: Diurnal Course of Efficiency. (Marsh) so 

(i) Description. In 1906, Marsh began a series of ex- 
periments at Columbia University dealing with the daily 
variations in mental, physical, and psycho-physical efficiency. 
His work attempted to find out whether there are normally 
recurring variations in ability during the day. Several 
groups of subjects were investigated for one or two days, 
and a few subjects for several days, among them seven grad- 
uate students, sixteen female undergradute students, twen- 
ty-two factory operatives and himself. In these tests he not 
only tried to find out what was shown in the laboratory by 
students, but also just what people accomplish under or- 
dinary conditions of life. As a rule, the tests were given 
four times daily, before breakfast, lunch, dinner, and bed- 
time. 

(2) Results. The results from his different tests will be 
presented separately according to the kind of test used. 

(a) Speed and Accuracy of Movement. In this test, 
which consisted of striking squares with a pencil point, 
an inverse ratio of speed and accuracy is shown, the 
most accurate tests being from 9 to 11 a. m., while the 
best speed was from 12 m. to 2 p. m. 

(b) Accuracy. In this test, which consisted of snap- 
ping a wooden disc at an opening 60 cm. distant, the 



DiURNAI. VARIATIONS ^t 

triost accurate results were made from 12 m. to 2 p. rri.^ 
and the least accurate were made from 4 to 6 p. m. 

(c) Speed. In this test for writing several words, the 
results show the best speed from 12 m. to 2 p. m., and 
the poorest from 4 to 6 p. m. 

(d) Tapping. These tests show a maximum rate frorri 
9 to 10 p. m., with the greatest accuracy about the mid- 
dle of the day. 

(e) Dynamometric Grip Tests. These were taken by 
Marsh for 30 days with great regularity oi external 
and subjective conditions, using the Collins Dynamo- 
meter. The average of grips taken with the right hand 
is shown in the table. 

7:008:30 10 11:30 1:30 3 4:30 6 7:30 9 10:30 11-12 
60.6 63 64.3 66.2 65.5 66.2 66.7 69 65.4 66 62.8 60.7 

The results show a rise to 11 130 a. m., a sli ?,ht drop 
at I 130 p. m., a second rise with a crest at 6 p. m., fol- 
lowed by a decrease to 11 p. m. 

(f) Work in Factories. In these tests, women factory 
operatives show a low morning power which increases 
till II a. m., falls slightly till i p. m., increases to a 
maximum between 3 and 5 130 p. m., and falls till bed- 
time. 

(g) Discrimination. In the tests for discrimination, 
the best ability was found at noon, and the poorest at the 
extreme periods. The shortest time was from 12 m to 
2 p. m., while the poorest was from 9 to 11 p. m. 

(h) Mental Tests. Mental tests were made in associa- 
tion, memory, and addition, all of which showed that 
from 12 m. to 2 p. m. was the most favorable, and 9 to 
II p. m., the least favorable. 
(3) Conclusions. For physical abilities including work 
in factories, there seems to be a gradual increase from the 
early morning hours in tests till 6 p. m., and in work till 



52 PERIODIC VARIATIONS IN EI^FICI^NCY 

about 3 to 5 p. m., followed by a decrease in both cases to 
II p. m. 

For mental abilities, the tests show a midday maximum of 
accuracy. The morning is favored though but slightly. In 
the strictly mental but more complex activities there is a 
similar inclination to the morning period both in rate and 
accuracy. 

(4) Criticism. In this work, the author employed a 
great variety of means in testing mental and physical effi- 
ciency. While the physical tests are quite well worked out, 
the data are rather weak on the mental side. The chief criti- 
cism is that the author drew his conclusions from too small 
an amount of data. His work should have been more ex- 
tended, and more daily records should have been made each 
day to give his conclusions the degree of validity assumed. 
However, the author used the methods which were consid- 
ered best at the time, in making his tests, and there has been 
but little improvement in the methods since his work, so that 
it still remains the standard work on the diurnal course of 
mental and physical efficiency. 

4. Diurnal Variations and Exercise Effects. (Leh- 
man AND Pedersen)25 

(i) Diurnal Variations. Lehman made tests to discover 
diurnal variations during a period of four days, and his re- 
sults are shown in the following table : 

9 A. M." (after breakfast) 32.5 Kilos 

I P. M. (before a 2-hour walk) 31.8 

3 P. M. (after a 2-hour walk) 35.3 

II P. M. (before retiring) 30.9 

(2) Exercise. Pedersen made a similar series of tests. 
taking a walk of from 2 to 4 hours duration at different 
times of day with the following results : 



DIURNAL VARIATIONS 53 

On level ground On rising ground 
Record made before walk 37.2 Kilos 36.8 Kilos 

Half way 37.8 " 

Top of rising ground 37.9 

Record made on return 38.0 " 38.4 

The first of these shows the influence of the time of day, 
while both show the beneficial effects of the two hours' walk. 
They also show that only those tests taken in the morning 
before work are rigidly comparable, as the kind of work done 
during the day has its effects on the results. The greater 
increase in muscle strength on the high ground, shows the 
beneficial effects of lowering the atmospheric pressure. 

5. Diurnal Variations in Muscular Enlrgy. 

(KUHNSS)21 

(i) Description. Kuhnes, whose work I have already 
reported under "Seasonal Periodicity," made a thorough in- 
vestigation of diurnal periodicity as shown in muscle 
strength. Each day, for 505 consecutive days, he took three 
tests with each hand in three different positions, alternately 
with the right and left hand, seven times daily, making in all 
twenty-one tests with each hand each day. The tests were 
very carefully controlled, and in order to eliminate the ef- 
fects of holding the dynamometer in different positions, the 
three positions were always the same and taken in the same 
order, viz. — (i) each hand hanging down, (2) each hand 
held vertically, and (3) each hand held horizontally. 

(2) Results. The results cover about 26,500 measure- 
ments, and the averages are somewhat as follows : At 7 a. m. 
comes a relatively low measurement followed by a rapid rise 
at 9 a. m., a slight drop at 12 m., a small rise at 2 p. m., 
which is the best time of all, a small drop at 6 p. m., a shght 
rise at 8 p. m. and a decided drop at 11 p. m. The average 
results for each hour during the whole period is shown in 
the accompanying table, ■ 



54 PERIODIC VARIATIONS IN e:^:?ICIE:nCY 





7 a.m. 


9 a.m. 


12 m. 


2 p.m. 


6 p.m. 


8 p.m. II 


p.m. 


Average 


43.5 


46.5 


46.5 


46.8 


46.5 


46.7 


45-3 


Maximum 


49 


50.6 


52.0 


50.8 


50.8 


5I.I 


50.6 


Minimum 


38.5 


39 


36 


41.5 


40.8 


43-0 


40.6 


Diff. of Max. 
















and Minimum 


10.5 


11.6 


14 


9-3 


10 


8.1 


10 


Median 


43.6 


46.8 


46.7 


47.1 


46.9 


47.3 


45.9 


Mean Variant. 


1.5 


1.7 


1.8 


1-7 


1-7 


1.8 


1.8 



(3) Conclusions. There is a distinct diurnal course of 
efficiency which starts low, rises till 12 m., drops slightly, 
but rises again showing its crest at 2 p. m. In the after- 
noon there is a drop at 6 p. m., a small rise at 8 p. m., fol- 
lowed by a rapid decrease till 11 p. m. The average curve 
here described is also the curve of 68 per cent, of the 505 
days. 

From the valuable introspections which he kept each day. 
he concludes that physical fatigue or physical inactivity cause 
a marked decrease in physical strength, while mental fatigue- 
has an influence that differs from that shown by physical 
fatigue. 

(4) Criticism. This work has been criticised before, 
but I will add here that it is the most complete record of diur- 
nal efficiency covering a long period of time, which has ever 
been made. All the data are given in complete f'^rm, and a 
most careful search fails to show any errors in the method, 
or in the interpretation of the results. 

6. Variations in Efficie:ncy During the Day. (Gates) ^^ 
(i) Method. During the year 1913-4, while a student at 
the University of California, Gates attempted to discover 
diurnal rhythms of efficiency by a variety of mental and 
physical tests. The subjects were pupils of the fifth and 
sixth grades in the public schools. During the five days of 
the tests, each class was divided into five groups of about 
eight pupils each. Each group was tested separately at 
9 a. m., 10 a. m., 11 a. m., i p. m. and 2 p. m. On each suc- 
ceeding test day, each group except that tested last was 
tested one hour later than before, while the one previously 



DIURNAL VARIATIONS 55 

tested last, was tested first. In this way each group was 
tested at a different hour each test day, and once at each of 
the hours mentioned above. 

(2) Results. The table here given show the combined 
record for all six classes in per cent., the first record being 
used as a base. 



Hours 


9-10 


lO-II 


11-12 


1-2 


2-3 


Addition tests 


100 


102.4 


104.2 


102.3 


103 


Multiplication tests 


100 


101.9 


105.1 


100.9 


103 


Auditory Memory 


100 


105.9 


106.7 


99.4 


102.4 


Visual Memory 


100 


103.2 


109.2 


99.06 


103.4 


Recognition tests 


100 


104.7 


105.9 


100 


103.7 


Maze Test— speed 


100 


100.34 


100.93 


108.9 


112.2 


Maze Test accuracy 


100 


102.9 


104.2 


98.2 


96 


Completion tests 


100 


105 


109.7 


106.2 


108.8 


Cancellation tests 


100 


101.8 


104.4 


194.9 


105.5 



Summarizing the results we find that in the addition, 
multiplication, memory, recognition, and completion tests 
there is a more or less steady rise in efificiency from 9 a. m. 
to noon, followed by a decrease of differing but always 
noticeable extent at i p. m. and a subsequent rise during the 
last hour. 

In the speed and accuracy tests, and in the cancellation 
test, there is a steady rise through the day with a maximum 
at the end. Speed is greater, but accuracy less in the after- 
noon, therefore it would seem that speed is attained at the. 
expense of accuracy. 

All of the functions tested show improvement due to prac- 
tice effects, varying from 7 to 33.3 per cent. There are no 
sex differences, or effects of fatigue, temperature changes, 
humidity, or weather in general shown in this study. The 
author finds high correlations only in the two arithmetical 
and in the two memory tests, while in the others, the cor- 
relations except in related functions do not amount to 
much, and that in such dissimilar tests the correlation re- 
sults are largely a matter of accidents. 



56 PERIODIC VARIATIONS IN I^FFICIKNCY 

He concludes that the strictly mental activities are more 
affected by fatigue than are the motor activities or those 
which involve muscle strength, the first showing a maximum 
in the late afternoon while motor functions show a contin- 
uous increase throughout the whole school day. 

(3) Criticism. The account of this investigation is well 
written and the author shows a broad and comprehensive 
knowledge of the work of other investigators in similar and 
related fields. In the tests used, in nearly every case the 
time given was far too short for all the children to perform 
the tasks demanded, so that after the children found out 
they could not do all of any test within the time limit, haste 
was probably a prolific source of error. It seems also that 
while the tests covered a great variety of functions, they 
were too few in number to warrant any universal conclu- 
sions, and it is to be regretted that preliminary and verifying 
tests were not made. However the author recognizes the 
limitations of his results, and does not draw any fanciful con- 
clusions which are unjustified by the results. The range of 
the tests and the care with which they were given, gives 
much validity to the results, which agree closely with those of 
other American investigators in this field. It is easily the 
best of its kind, and it must be taken into account by all 
future investigators of diurnal variations in mental abilities. 

7. Diurnal Variations in Mkmory and Association. 
(Gates) 12 
(i) Method. Gates supplemented his first investigation 
by a series of memory and association tests made on groups 
of from six to fourteen college students, numbering 165 in 
all. The tests were made at each hour of the day from 8 
a. m. to 5 p. m., excepting only the noon hour. Before taking 
the tests each student was asked to state, among other 
things, the .time of day when he felt he could do his most 
and best work. Tests were given in auditory memory, 



DIURNAL VARIATIONS ^7 

visual memory, substitution, recognition, and logical mem- 
ory (Healy Test). 

(2) Results. The average results in per cent for each of 
the various tests is here given. 

Hour 89 10 II 12 3 4 5 

Auditory memory 100 97.5 98.8 103.3 97-4 94-5 98.2 95.5 93 8 

Visual memory 100 99.3 101.5 101.5 98.0 loo.i 101.7 102 100 

Substitution 100 102.7 195.2 104.3 96.0 102.6 101.5 101.2 94.3 

Recognition too 115.7 122.2 115.7 106.5 m 120 120 116.5 

Logical memory 100 109 T07.7 103 95.5 99.3 10 1.4 102.2 91.3 

Avg, of all tests 100 104.3 106.6 105.6 98.7 100.6 105. i 104.2 100.4 

The results from all these tests show a great similarity. 
Beginning at 8 a. m., all the curves rise till 10 and some till 
II a. m. The i p. m. figure is quite low in all tests and al- 
ways lower than the late afternoon. 

(3) Conclusions. In the subject's own estimates of their 
best hour, many choose too early an hour, few choose 10 
a. m. or II a. m., and practically none choose the late after- 
noon hours. From this Gates draws the conclusion that 
one's subjective feelings with regard to the time of greatest 
efficiency, are not reliable. The hours of greatest efficiency 
are those at which fatigue (it would seem), should be very 
great. A man should, therefore, by practice in the voluntary 
disregard of the mere feelings of fatigue learn the limits of 
his ability and thus attain greater efficiency. 

(4) Criticism. In this series of tests the author used sev- 
eral well known methods for testing efficiency in the field of 
immediate memory and association. The invcstie-ation 



IS 



valuable chiefly from the fact that such a large group (165 
college students) were given such a variety of tests for pur- 
poses of comparison. It is to be regretted, however, that the 
experiments lasted only three days, and that on the days 
mentioned, the subjects spent the time in continuously taking 
tests. The questionnaire submitted to each student before 
taking the tests, brought out some very interesting facts, and 



58 PI^RIODIC VARIATIONS IN E^Fl^lCI^NCY 

shows one's own opinion of his best working hours is not 
reliable. 

8. Summary oi^ Problems and Rksui^ts in Diurnal 
Periodicity. 

The diurnal course of efficiency seems to be pretty well 
established both for mental and physical abilities. In both 
cases, all previous investigators have found both a morning 
and an afternoon crest. The records for variations in phy- 
-DBj u] y[JiOM. puB sapTApoE jo;oiu .ouipnpui 'S3p[|iqi: jeois 
tories, show a continuous increase in the morning till about 
II a. m., a slight drop from 12 m. to i p. m., with a further 
rise to a maximum sometime between 3 and 6 p. m. The 
results for mental work show a more or less steady rise till 
II a. m., a slight drop around noon with a new high level 
around 2 p. m., then a gradual decrease till the close of the 
day. Kuhnes found that in many cases physical strength 
grows continuously till about 8 p. m., after which it declines. 
This fact was also noted in some factory workers by Marsh. 

In Speed and Accuracy Tests, accuracy is better in the 
morning and speed greater in the afternoon, a result which 
seems to show that speed is often gained at the expense of 
accuracy. 

Kuhnes found in a test covering 505 consecutive days that 
the average daily curve in dynamometric tests is also the 
curve for 68 per cent, of the days. This would seem to indi- 
cate the great importance of diurnal variations in any study 
of seasonal periodicity. 

9. Diurnal, Periodicity in My Original Experimental 
Investigation. 

In my own investigation, through October, November and 
December, the B. division was tested at various hours from 
9 a. m. to 3 p. m. After January the tests were always given 
between 2 p. m. and 3 p. m. The following table shows the 
distribution of variations i Kg. from the weekly average in 
grip strength. 



12 


12 


12 


30 


30 


5 


10 


15 


35 


35 


30 


20 


10 


20 


20 


5 


4 


3 


I 


2 



DIURNAL VARIATIONS 59 

Hour of the Day 9 to lo lo to ii ii to i2 i to 2 2 to 3 

Per cent, of tests given 

at each hour 20 8 8 24 40 

Per cent, of test varying 
I Kg. from the average 
I Kg. above the average 
I Kg. below the average 
Rank 

These data seem to shov^ a diurnal course of efficiency 
which rises continuously from 9 a. m. to 3 p. m. for muscle 
energy. The exceptionally low records made at 10 to 11 
a. m. and at i to 2 p. m. were made during the first week. 
There was no test made at 9 a. m. until Monday of the third 
week, so we find these low records at the other hours. In 
spite of this fact, however, the average of the 9 a. m. records 
is the lowest of all the hours shown as can be seen in the 
following table : 

RIGHT HAND LEFT HAND 

Hour 9-10 lo-ii ii-'i2 1-2 2-3 Hour 9-10 lo-ii 11-12 1-2 2-3 

Avg. 47.7 48.8 48.9 49-3 51-^ Avg. 44.5 44.7 45 46 46.3 

High 50.1 54.3 54.4 55.3 57.1 High 46.6 49.9 50.4 5i 53-6 

Low 43.7 43.3 46.1 42.6 43.0 Low 42.3 39.5 41 42.4 40 

These results agree with those of other investigators in 
showing muscle energy increases almost continuously from 
9 a. m. to at least 3 p. m. 

The results for memory show a similar tendency except 
for a greater depression from 11 a. m. to i p. m., as can be 
seen from the following: table : 





MEMORY FOR 15 : 


NUMBERS 






Hour 
Average 
High 
Low 


9-10 lO-II 
lo.i 10.7 
10.9 II.7 

9.5 8.3 


11-12 
10 
11.2 
8.2 


I-{2 
10. 1 
II.9 

8.8 


2-3' 
10.5 
11.6 
8.8 




MEMORY FOR 4 NUMBERS 






Hour 
Average 
High 
Low 


9-10 lO-II 
3.56 3.65 
4 3-9 
2.5 3.3 


11-12 
3-45 
3.8 
2.8 


1-2 
3.64 
4 
3.2 


2-J 

3.68 

4 
3.3 



6o PERIODIC VARIATIONS IN KFFICIKNCV 





MEMORY 


FOR 5 


NUMBERS 






Hour 


9-10 


lO-II 


11-12 


1-2 


2-:^. 


Average 


3-32 


3.65 


3.03 


3.47 


3.34 


High 


3.7 


4-3 


3.3 


4.6 


3.9 


Low 


2.9 


2.5 


2.8 


2.6 


2.8 




MEMORY 


FOR 6 


NUMBERS 






Hour 


9-10 


lO-II 


11-12 


I-(2 


2-3. 


Average 


3.2 


3.4 


2.9 


3.1 


3.5 


High 


4-1 


4 


3.8 


3.9 


4.3 


Low 


2.9 


2.5 


2.3 


2.5 


3.4 



In all probabilit;/ the results for the series of five numbers 
aie the most reliable. The series of four numbers served 
as a sort of preliminary test to fix the attention on the task, 
and to warm subjects up to the work. The series of six 
numbers was perhaps too long, a perfect score being very 
rarely made. These results for primary memory all show a 
rise from 9 to 11 a, m., a drop from 11 a. m. to i p. m., a 
rise from i p. m. to 2 p. m. and a slight drop from 2 to 3 
p. m. in some cases, while in other the records from 2 to 3 
p. m. remain almost stationary. The results from the A. 
division were almost all made between 2 and 3 p. m., so that 
they add nothing to the results on diurnal periodicity. 



CHAPTKR V. 

OTHER PERIODIC VARIATIONS IN MENTAL AND 
PHYSICAL ABILITIES 

(i) Introduction. Besides the diurnal and seasonal vari- 
ations, there have been many other suggestions as to periodic 
variations in mental and physical abilities. Among those we 
find the so-called Twenty-eight Day period, the Twenty-three 
Day period, and the Seven Day or weekly period. 

(2) Tzventy-cight Day Periodicity. Malling-Hansen 
first suggested that vital force was subject to periodic varia- 
tions every twenty-eight days. Of course there is no doubt 
about the twenty-eight day periods in females, but the exist- 
ence of twenty-eight day periods in mental and physical 
abilities has never been firmly proven or disproven as yet. 
This is due to the fact that such periods would vary with 
the individuals and investigators have been much more in- 
terested in results from large numbers than from individuals. 

Dr. Kuhnes has given this problem more attention than 
any other investigator. In this investigation in variations in 
physical ability, he arranged the data in a series of thirteen 
twenty-eight day periods, counting twenty-eight day periods 
from the day of his birth. His results when so arranged, 
show a marked variation through the first three days, an 
.almost constant value from the fourth to the twentieth, and 
more or less irregularity from the twenty-first to the twenty- 
eighth day. The highest points are found on the twenty- 
second, twenty-third, and twenty-fourth days, while the low- 
est point is found on the third day. Dr. Kuhnes comes to 
the conclusion from his remarks that they gave little warrant 
for assuming the existence of a twenty-eigTit day period in 
muscle strength. 

61 



62 PKRIODIC VARIATIONS IN E;FFICIE:NCY 

My own data are not arranged in a suitable form for a 
comparison with the results of others as to the existence of a 
twenty-eight day rhythm. 

(3) Tzventy-thrce Day Periodicity. Stohr describes 
briefly a Twenty-three Day rhythm found independently by 
two Germans, Fleiss and Svoboda. Each of these men claim 
to have found a twenty-three day period in mental and phy- 
sical abilities on the basis of personal observation, Svoboda 
claiming that ideas automatically and spontaneously re- 
appear in the mind every twenty-third day. 

So far as I know, no American investigator has found 
similar results. Dr. Kuhnes arranged his data in twenty- 
three day periods counting from birth. His curve for aver- 
ages shows a nearly straight trend for 17 days, then rises 
slightly till the end of the 22 day, and shows a rise of seven 
kilos on the twenty-third day. This variation is nearly 
double the rise and fall on any other day. The median curve 
shows a gradual decline until the tenth day, a sudden drop 
on the eleventh day, with a gradual rise to the end of the 
period. The 9 a. m. records show a- distinct rise on the 
twenty-third day, but the point reached is not higher than 
that on the fourteenth day. He concludes that while there 
are some unexpected peculiarities in his results for the 
twenty-third day, his data do not warrant a general ac- 
ceptance of the twenty-three day period. 

In this field, as in the twenty-eighth day period, my own 
data cannot be arranged in a way that would be comparable 
with the results of others, or to show any twenty-three day 
periods. 

(4) Weekly Periodicity. 

(i) Introduction. Weekly periodicity has not been in- 
vestigated to any considerable extent. The fact that for 
many generations people in many lands have ordered their 
lives by seven day periods would suggest the possibility of a 
seven day period in mental and physical abilities. 



OTHER PERIODIC VARIATIONS 63 

(2) HuHtingfon^^. Huntington found that on the whole, 
the curves of work done by piect-workers are higher at the 
end of the week than at the beginning, Monday being low, 
and Thursday and Friday the highest, with a falling off on 
Saturday. He gives the following table for piece-workers 
in a Cuban factory. 

Mon. Tues. Wed. Thur. Fri. Sat. 
81.9 98.7 99.8 100 98. 97.9 

(3) Kuhnes?'^ Kuhnes studied the averages of 42 daily 
tests for fifty-three weeks with the following results : 



Days 


Sun. 


Mon. 


Tue. 


Wed. 


Thu. 


Fri. 


Sat. 


Average 


46 Kg. 


45.9 


46.3 


46.1 


45.9 


46 


46.3 


Maximum 


49.1 


49.3 


49.5 


48.9 


48.7 


49 


48.9 


Minimum 


42.9 


42.0 


43.2 


43-1 


41.5 


42.8 


43-2 


Diff. of M-M 


6.2 


7-2 


6.3 


5.8 


7.2 


6.2 


5.7 


Mean Var. 


1.53 


1.66 


1.43 


1.34 


1.31 


1-53 


1.33 


Median 


45-5 


46.1 


46.6 


46.3 


46.1 


45.8 


46.3 



In this table, Mondays and Thursday show the lowest 
averages being 4 kg. below the maximum reached on Tues- 
days and Saturdays. Kuhnes found that the weekly curve 
followed very closely that of the days of the most and least 
study, and that hard study with a lack of exercise caused 
low records. 

5. Weekly Periodicity in My Original Experimental 
Investigation. 
In an endeavor to discover any traces of a weekly period 
in my own results, I first tabulated the daily distribution of 
the averages i Kg. from the averages for the week, and 
give them In the following table in per cent. 



Day 


Right Hand 

Above Below 


Above 


Left Hand 
Below 


Rank 


Monday 

Tuesday 

Wednesday 

Thursday 

Friday 


9 .18 

12 12 

9 

9 

19 12 


6 


II 
9 

16 


25 
16 

3 

3 

II 


5 
4 
2 

I 
3 



64 



PERIODIC VARIATIONS IN l^FFlClENCY 



These results show that Monday is the poorest day while 
Thursday is the best. Monday and Friday are more variable, 
but on Monday the variations tend to fall below the line of 
weekly averages, while on Friday they tend to rise above it. 
The number of such variations on Wednesday and Thursday 
is small, and almost all of them are above the average for 
the week. 

According to these data, ^Monday is low, and is followed by 
an irregular rise through the week to a crest on Thursday. 
This is followed by a slight drop on Friday. The following 
tables show the results for the Memory and Grip Tests b_v 
days for each month. 









GRIP TABLE 








Day 




Mon. 


Tiie. 


Wed. 


Thn. 


Fri. 


Oct. 


R. 


45-2 


-^6.6 


46.4 


45.8 


45.6 




L. 


42.1 


41.7 


43-2 


43 


42.6 


Nov. 


R. 


50.8 


49.6 


50.4 


49-3 


48.9 




L. 


47.2 


46.7 


47-2 


45-4 


46.5 


Dec. 


R. 


53.5 


53.4 


SI.6 


52.3 


527 




L. 


50.6 


48.6 


49.2 


497 


49.7 


Jan. 


R. 


534 


54-2 


54-7 


54-5 


54.6 




L. 


50.8 


5I.I 


517 


50.8 


51-3 


Feb. 


R. 


54 


54 


54-4 


54.2 


54-2 




L. 


51 


50.7 


507 


514 


51-9 


Mch. 


R. 


547 


54.6 


56.5 


56.2 


57.3 




L. 


52.4 


53 


52.8 


52.9 


52.5 


Apr. . 


R. 


55-2 


56.4- 


56.5 


56.2 


57-3 




L. 


53.6 


54.7 


52.6 


54-2 


54-3 


May 


R. 


58.3 


59.1 


59.1 


58.9 


56.3 




L. 


53.6 


55-4 


55-9 


55-2 


54.9 




MEMORY TABLE (i 


5 points) 






Oct. 




10.2 


8.8 


9 


97 


9.6 


Nov. 




10 


II. I 


10.4 


19.1 


lO.I 


Dec. 




II. I 


II 


10.8 


10 


II 


Jan. 




10.3 


10.3 


10.4 


10.3 


II 


Feb. 




9.8 


9-9 


10.3 


10.5 


10 


Mch. 




10.9 


10.9 


10 


10.3 


19-3 


Apr. 




11.6 


11.6 


10.7 


114 


10.6 


May 




11.4 


II. I 


II 


1 1 -5 


11.6 



OTHKR PKRIODIC VARIATIONS 65 

The table for memory does not show any pronounced 
weekly periodicity for all the months of the year. In Oc- 
tober, December, March, and April, the first part of the 
week seems to be more favorable, but in January, February, 
and May the reverse is true. In November the middle of 
the week. seems preferable. 

The results from the Dynamometric Tests show a similar 
lack of any weekly periodicity. In November and Decem- 
ber, the early part of the week is preferable, but in February 
and April, the opposite is true. Wednesday is very favorable 
in October, November, January, and May, while in March 
there does not seem to be much choice. From the data as 
presented, therefore, we are not warranted in assuming that 
there is any weekly periodicity shown either in the mental or 
physical tests. 



CHAPTER VI. 

WEATHER INFLUENCES 

(1) Introduction. Many statements have been made in 
literature about the effects of various kinds of weather on 
human thought and action, but very httle has been done to 
test these opinions in a scientific way. Of late, two or three 
investigators have attempted to discover some existing rela- 
tions between the variations in the amount of sunshine, tem- 
perature, humidity, and air pressure on the one hand, and in 
the physical, mental, and moral life of the individual on the 
other. One writer, Huntington, points out the very close 
relation between various types of civilization and climatic 
conditions, and concludes that climatic conditions are as 
important factors in civilization as are the oceans, lakes, 
rivers, mountains, and natural resources. 

While the author does not expect to come to any unusual 
conclusions in this regard, the results as here shown may 
give additional proof to facts already well established. The 
first task, however, will be to give a brief review of the 
work already done in this field. 

(2) General Weather Effects. 

(a) Conduct and the Weather. (Dexter).'^ 
The first American to investigate the effects of the 
weather to any extent, was Dexter, who tried to study the 
relations of conduct and the weather. The questionnaire, 
supplemented by various public and private records on 
crime, insanity, and school conduct, and the U. S. Govern- 
ment records on weather conditions were used as sources for 
the data. In each case the relationship established is purely 
statistical, based on the probability or expectancy of occurr- 
ence, all the data being arranged to show the actual distribu- 
tion of the occurrence, as compared to the expected distribu- 

66 



WEATHER INFLUENCES 67 

tion of the occurrence. In this study were included data from 
the records of attendance and discipHne in the public schools 
of New York City and Denver, police records of Assault 
and Battery, Murder, Insanity, Suicide, and Death ; Clerical 
Errors in a number of New York City banks, and data 
from laboratory experiments made at Columbia University. 
These are compared with government records of tempera- 
ture, humidity, wind, and character of the day. 

(i) Results. The results, with complete descriptions of 
the data, tables, and graphs, are described in detail, and from 
them the following general conclusions are drawn : 

I — Males are more influenced by weather conditions 
than females, and boys are more influenced than girls. 
2 — Precipitation has little or no effects at all. 
3 — Barometric changes influence largely through the 
production of other states of weather, rather than directly. 
4 — Medium conditions of humidity are more favorable 
than extremes in either direction. 

5 — Time of year has no marked effects on conduct. 
6 — Varying weather conditions affect directly the meta- 
bolism of life. 

7 — Reserve energy is influenced to a marked degree by 
weather conditions. 

8 — The quality of emotional states is plainly influenced 
by the weather. 

9 — Conduct, death, physical labor, and intellectual ac- 
tivities, bear very different relations to reserve energy. 

10 — Those weather conditions which are productive of 
misconduct, in a broad sense of the word, are also pro- 
ductive of health and mental alertness, and 

II — Misconduct is the result of an excess of reserve 
energy not directed to more useful purposes. 
(2) Criticism. The aim of this investigation was a very 
worthy and necessary one, and while the method of select- 
ing the data might be improved upon, the author had a vast 



68 PERIODIC VARIATIONS IN EFFICIENCY 

amount of materials at his disposal. The chief defect is 
that only statistical use was made of the data. In this way, 
the only thing that can be indicated is the statistical com- 
parison between the expected and the actual occurrence of 
phenomena, all the discussions and conclusions being based 
on this artificial relationship. What is shown is a probable 
relationship based on a statistical estimate of the occurrence 
of phenomena, rather than any actual relationship between 
the variations in the phenomena. In this way the actual 
effects of changes in the temperature, humidity, air pres- 
sure, as well as those of unusual combinations of atmospheric 
conditions are almost entirely unnoticed. Then again, the 
data from the questionnaires, should have received little 
weight unless the opinions expressed were supported by rec- 
orded observations, as many instances have been shown 
where the opinions of individuals are contrary to the real 
facts. We should, therefore, exclude that part of the re- 
sult which is based on such data. In the light of these fact? 
it will not do to give too much weight to his results and 
conclusions. We must, however, recognize that this is a 
pioneer work, and give it credit for being what the author 
claims for it, "A modest contribution to the knowledge on 
the subject." 

(b) Civilization and Climate. ( Huntington ).^^ 
Huntington discusses many phases of weather and climate 
in its relation to civilization and to the activities of mankind 
in general. Incidentally, the author collects such data con- 
cerning the influence of the weather on the quantity of work 
done by factory workers in various parts of the United 
States and Cuba, and gives his results. Among factory 
workers in New Haven, the lowest point of efficiency is in the 
last half of January. It rises slowly to June, drops slightly 
through July and August, rises ([uickly in September, and 
culminates around the first of December, 



we:athe:r infivUe:nce:s . 69 

He gives several graphs of work done by factory workers 
in various parts of the United States, all of which are similar. 
Further south the culmination comes a little later in the sea- 
son and varies from sometime in November in New Haven, 
to the middle of December in South Carolina and Florida. 
Southern workers also show a disposition to hold the high 
level till about the middle of January, while farther north 
they show a decrease in working capacity somewhat earlier. 
(c) Effects in Weather on Ability to Learn. ( Lehman) ^^ 
Lehman conducted a series of tests to discover the effects 
of weather on ability to learn rows of syllables by heart. 
The subjects were several university students and the tests 
lasted from October, 1905, to March of the following year. 
A device was used which allowed but one syllal^le to be 
visible at a time. One hundred thirty rows of 16 syllables 
each were prepared. Each syllable was presented for .75 
seconds and the full rows were presented at intervals of 
three seconds. The subjects were scored on the number 
of repetitions necessary before being able to give a perfect 
reproduction of the row. The results appear in the follow- 
ing table : 

Sep. Oct. Nov. Dec. Jan. Feb. Mch. Apr. May Jun. 
518 521 559 528 618 555 612 549 642 553 

This shows a rise to a high level in January, a drop for 
February, a quick rise- in March, and a culmination in May. 
From these data he concludes that the variations of memory 
agree much better than those of muscle strength with those 
of air pressure. The curve swings up and down during No- 
vember and December, but shows a rise in January. In con- 
clusion he says that memory is probably influenced in the 
same way as muscle strength by metreorological conditions. 
(3) Effe:cts of Variations in Sunlight. 

Though the exact eft'ects of sunlight on the human organ- 
ism are unknown, much has been written about its stimu- 



yo PE^RIODIC VARIATIONS IN EF'FICIKNCY 

lating effects, and we have all felt its power. Dexter sug- 
gests that sunlight and clear days cause an excessive amount 
of "reserve energy" which must be worked off. In this way 
he accounts for the excesses of assaults, murders, and sui- 
cides on sunny days. In his study he also finds that there are 
fewer errors in banks on sunny days, indicating that sunny 
days are more favorable to mental work than cloudy days. 

Lehman and Pedersen after a thorough and systematic 
investigation of the effects of sunlight on muscular ability 
come to the conclusion that next to temperature, the effects 
of light on muscle strength are more pronounced than any 
other one cause. They measured light strength with a 
Steenstrup Photometer and found that muscle strength 
begins to rise in January with light strength, and continues 
to grow with it until July when the good effects are over- 
come by the bad effects of excessive summer heat. 

(4) Effects of Changes in Ti:mpe;r.\ture. 

( 1 ) Introduction. Perhaps the most important influence 
of all the varied weather conditions is that of temperature. 
The effects of extremes of heat- and cold are well known. 
If our bodies are too long exposed to a low temperature 
without protection, the nervous system becomes paralyzed 
and death ensues. If our body is exposed to extreme heat 
for too long a time, discomfort, sleepiness, and finally a heat 
stroke results. 

(2) Body Temperature. In any study of heat effects 
on human life, however, the body temperature is perhaps the 
most important factor. In spite of many external changes, 
this remains fairly constant. The temperature of the air 
surrounding the body under our clothing is about 90°. We 
keep this fairly constant by wearing a greater or less amount 
of clothing. The average body temperature remains con- 
stant at about 98.6° F. or 36° Cent. This varies with in- 
dividuals, and with the same individual on different days. 



We:aThe:r iNr^LUKNCKS 71 

(3) Benedict and Carpenter, ^ These investigators found 
a minimum body temperature from 3 to 5 a. m., a marked in- 
crease at about 7 a. m., a slow, steady rise through the 
evening to the minimum at from 3 to 5 a. m. They also 
found variations in the body temperature of one subject to be 
2.29° F. on the first day, and 1.67° F. on the second day. 

(4) New York Commission. This commission found 
that the body temperature of subjects living at home at 8 
a. m., was high if the preceeding night had been warm, and 
low if the preceeding night had been cool. The variation was 
about I ° F. for 20° F. of atmospheric temperature. 

(5) Burnham.5 Burnham says that with an increase in 
the external temperature there is likely to be a rise in the 
bodily temperature, and this is accompanied by an increase 
in metabolism. Up to a certain optimum, this increases the 
activity and the efficiency of the organism, beyond that, the 
increase in metabolism caused by increase in temperature 
brings about a condition where the oxidation and elim- 
ination processes are not sufficient to carry off the 
waste products, with the necessary rapidity, toxic products 
accumulate, and thus fatigue comes quickly. Re- 
cent studies indicate that the cause of heat stroke and sun 
stroke is an abnormal change in metabolism. 

(7) Dexter."^ Dexter reports that in New York City/ 
when school room temperature was below 68° F., the mis- 
demeanors were below normal, from 69° to 73° F. they were 
about normal, while in a temperature of 79° F. they were- 
below normal. 

(8) Hines.is Supt. Hines, of Crawfordsville, Ind, re-, 
ports the following in regard to the effects of various class- 
room temperatures : 

80° F., Class restless and dull. 70° F., Excellent work. 
74° F., Not so dull as above. 68° F., Best work today. 
72"" F., Restless. 66° F., Splendid work. 



*J2 PERIODIC VARIATTONS IN KFFICIKNCV' 

65° F., Class happy and full 60° F., Too cold for good 
of work. work. 

(a) Influence of Temperature on Rapidity of Addi- 
tion. (L. and P.)^^ 

From May, 1906, to February, 1907, both Lehman and 
Pedersen took daily tests in rapid addition each morning 
either before or after the dynamometric measurements, 
there being seven columns of 50 one place numbers in each 
test. The results were then compared with variations in air 
pressure, light strength, and temperature. The conclu- 
sions are as follows : "Up to the present we have not been 
able to show any dependence of rapidity of addition on light 
strength or air pressure. As soon as the small variations are 
effaced by taking the averages for each five days, the re- 
maining variations show themselves almost entirely inde- 
pendent on temperature." The results are shown graphi- 
cally, and indicate that when temperature sinks, rapidity 
of addition rises, and vice versa, the variation in rapidity 
of addition beginning only after temperature variation has 
continued a short time. 

(5) Ef?e:cts of Variations in Humidity. 
The humidity of the atmosphere is very closely related to 
temperature in its effects on human life. It especially effects, 
the body in its efforts to maintain a constant temperature. 
One of the chief means for keeping the temperature of the 
body from climbing too high is perspiration. Whether this 
takes place at the proper rate depends as much on the hu- 
midity as on the temperature. Though the disagreeable 
effects of humidity on bodily comfort are well known, they 
have not been investigated apart from temperature to any 
extent. 

The New York Commission found that bodily tempera- 
ture was lowered by confinement in an atmosphere of 68° F,, 



WEATHER INFLUENCES 73 

with 50 per cent, relative humidity, that it was raised in an 
atmosphere of 75° F. with the same humidity, and raised still 
more in an atmosphere of 86° F. with 80 per cent, humidity. 
The same commission found the average pulse rate at 86° F. 
with 80 per cent, humidity to be 74, and at 68° F. with 50 
per cent, humidity to be 66. The report also says, "Eastman 
and I have seen the pulse rate increased by 39, form 67 to 
106, as the temperature of the surrounding air rose from 74° 
to 110° F., and the humidity rose from 50 to 90 per cent. 
(Page 185). 

All these facts would indicate that excessive humidity not 
only causes extreme physical discomfort, but that it has a 
more or less distinct and direct influence on mental and 
physical efificiency. 

Dexter's '^ findings seem to agree with the above. He 
found that a low humidity caused an excess of occurrence in 
nearly all classes of data studied, and vice versa. 

Kuhnes-^ found that among 8 students, the best work was 
done when the relative humidity was from 75 to 85 per cent., 
but when the relative humidity fell below 50 per cent, there 
was a marked drop in efficiency. 

Huntington^^ found that in winter, the dampest days are 
unmistakably the times of greatest efficiency. /^'*We may 
shiver when the air is raw, but we work well." The rea- 
son is two-fold. In general the temperature rises in times 
of excessive humidity and this of itself is favorable. In 
spring and fall when the temperature ranges from freezing 
to 70° F. with an average of about 50° F. the best work 
is done with a relative humidity of about 75 per cent. In 
other words, neither dry nor wet days are the best. The 
summer curve is a complex one. It rises first to a maxi- 
mum at 60 or 65 per cent., then falls, and once more rises to 
a higher maximum. The first maximum is due to humidity, 
the second to temperature. A hot, damp day is debilitating. 
The majority of the dampest days in summer are compara- 



74 PERIODIC VARIATIONS IN e;fficie:ncy 

tively cool for they accompany storms. The coolness coun- 
terbalances the humidity and efficiency increases. Hence, 
we conclude that with an average temperature of 60° F. to 
70° F., a relative humidity of about 60 per cent, is desirable." 
His curves also show a diminution of work in dry weather. 
This evidently has a bearing on the low level of the curve of 
energy in winter. At that season the air in the house is only 
V 16 to 20 per cent, relative humidity, and it should be 60 to 

J\^65 per cent. On cold days the percentage is still lower. It 
dries up the mucious membranes and is favorable to colds,' 
besides producing deaths in February and March. 

/Uj 6. Effects of BAROMSTiRic Changes. "-^ • 

There is much difference of opinion as to the effects of 
barometric changes. The general idea seems to be that of 
Dexter, who says that the general effect of high altitudes is 
undoubtedly an invigorating one. His investigation shows 
that with the sole exception of his study of Errors by Bank 
Clerks, a low barometer is favorable, while a pressure above 
the normal is unfavorable. 

Lehman and Pedersen on the contrary, found that muscle 
strength is so influenced by air pressure in the spring, that it 
rises and falls with the same, that it is independent of air 
pressure in the fall up to the end of November, that from 
December to March the variations agree more and more 
closely, and from April to June they seem to agree very 
closely. After June there seems to be no relation till De- 
cember. A change from a sea level to a height where air 
pressure is 99 mm. lower, has no influence on muscle strength, 
neither is muscle strength influenced by a continued stay at 
such a height. A return to the sea level, however, causes a 
more or less noticeable rise in muscle strength, according 
to the temperature, but it lasts only a short time. These ef- 
fects are shown in the following table, where the averages of 
the positive and negative deviations of muscle strength of 



we:athe:r influences 75 

Lehman on two different years, Miss J. and the Boys' class 
are compared with the barometric readings. 
Barometric Readings L 1905 L 1906 Miss J. Boys 
Above 763 +0.09 +0.28 +0.47 +0.15 

Below 762 — 0.03 — 0.17 — 0.44 — 0.49 

Kuhnes found that of 8 test persons, 6 were at their best 
when the barometer was .10 above normal, and one each 
at .10 and .20 below normal, though in each of these cases, 
the second best record was at .10 above normal also. It 
would seem, therefore, that a barometer slightly above nor- 
mal is beneficial to muscle strength. 

7. Summary of Problems and Results in Weather 
Effects. 

There seems to be very little doubt that both mental and 
physical energy is influenced by the character of the climate 
in general, wind, sunshine, temperature, humidity, and air 
pressure, though the exact effects are still somewhat uncer- 
tain. 

(i) Precipitation. Some authors find that precipitation 
has little or no effect. This is the view of Dexter. Hunt- 
ington finds that physical efiiciency is high at the close of a 
storm. 

(2) Winds. Dexter finds that calm weather results in 
decrease in vitality, while moderate winds and high winds 
cause vitality to increase to a certain point. Excessive 
winds cause a decrease in vitality. 

(3) Character of the Day. The effects of various kinds 
of days on mental and physical abilities seems to be con- 
trary to general opinion. Dexter suggests in one place that 
sunlight and clear days cause an excessive amount of re- 
serve energy, and must be worked off. In another he finds 
that for all the data studied, except deaths, sickness, and er- 
rors in banks, cloudy days are more favorable than fair days. 
He was surprised to find more suicides on cloudy days than 



76 PERIODIC VARIATIONS IN EFFICIENCY 

on days with precipitation, and more on fair days than on 
either of the others. 

Lehman and Pedersen found that next to temperature the 
effects of hght were more pronounced than any other cause. 
Huntington found that people are least efficient in work on 
clear days, moderately efficient on cloudy and partly cloudy 
days, and most efficient at the end of a storm. He also finds 
that ability to work on the first clear day is very poor, the 
second and third clear days are better, the first cloudy days 
when storms start are medium, and from the second to the 
last of a series of stormy days, when storms break, is very 
high. 

(4) Temperature. Changes of temperature are perhaps 
the most important of all atmospheric influences, and operate 
directly by causing changes in the body temperature. The 
body temperature must be kept fairly constant at about 
98.6° F. This has been found to vary slightly with different 
individuals and in the same individual on different days. 
Benedict and Carpenter, and another investigator, Polio- 
manti,^^ find a daily rhythm of body temperature, starting 
from the lowest point between 3 and 5 a. m., showing a sharp 
rise at 7 a. m. and a slow, steady rise through the day, cul- 
minating •between 3 and 6 p. m., then falling slowly to the 
minimum between 3 and 5 a. m. 

Lehman and Pedersen find that when the temperature 
sinks rapidity of addition rises, and vice versa, the variation 
of rapidity of addition beginning only after the temperature 
variation has continued a short time. They also suggest 
that each person has a temperature optimum differing for 
mental and for physical work, and that the abilities increase 
as the temperature nears the optimum either from above or 
below. 

Huntington located the optimum for physical work be- 
tween 59° and 65° F., while Lehman and Pedersen locate 



W'KAtHRR INFtUr.NCKvS 77 

theirs at 54° and 59° F, respectively. Students at Annapolis 
worked best when the outside air was 40° F. 

Burnham^ says, there is apparently an optimum tempera- 
ture for all forms of activity, fixing it in man at an outdoor 
temperature of 60° F. for physical activity, and at 40° F. 
for rnental activity. Concerning ventilation of school rooms, 
B-rairnham states that the primary purpose of ventilation is to 
maintain an optimum temperature, and concludes that the 
optimum temperature for a school room seems to be about 
68° F. with a relative humidity of about 50 per cent. 

(5) Humidity. Humidity especially affects the body in 
its efforts to maintain an optimum temperature by its in- 
fluences over the amount of perspiration. Huntington finds 
that in winter, the dampest days are best ; in spring and fall 
when the average temperature is about 50° F. we work best 
with a relative humidity of about 75 per cent. ; and in dry 
weather there is a diminution in the amount of work done. 

Dexter found that a low humidity caused an excess of 
occurrence of nearly all classes of data studied, and vice 
versa. Kuhnes found that the best work was done when 
the relative humidity was from 75 to 85 per cent. ; but when 
the relative humidity fell below 50 per cent, there was a 
marked drop in physical efficiency. 

(6) Barometer. The general opinion concerning the in- 
fluence of barometric changes seems to be that of Dexter, 
that a low barometer and high altitudes are favorable to 
mental and physical activities. On the contrary, Kuhnes 
found that a barometric pressure of about .10 above normal, 
with slight individual differences, seemed to be the most 
favorable, and Lehman and Pedersen also found an increased 
efficiency with high barometric pressure. They also found 
that a change from sea level to higher land has no influence, 
but that on a return to the sea level, a more or less noticeable 
rise occurs which varies with the temperature conditions. 
They claim that in the spring, muscle strength rises and falls 



y^ PERIODIC VARIATIONS IN EFFICIENCY 

with the barometer, that they separate in July, and are in- 
dependent till December, when they begin to agree more 
and more closely, coming into very close agreement in March. 

8. Weather Effects in My Original Experimental 
Investigation. 
(i) Character of the Day. In order to study the effects 
of the general character of the day I have used the U. S. 
Government Weather Reports and arranged the days of the 
month under the three heads of clear, partly cloudy, and 
cloudy in the accompanying tables. 

AVERAGES OF RIGHT HAND GRIPS 

Month Oct. Nov. Dec. Jan. Feb. Mch. Apr. May 

Clear Days 45-8 49-8 52.5 53-8 54-2 54-6 55-9 58.8 

Ptly. Cldy. 46.2 50.5 54.9 53-8 544 55 56-9 59.6 

Cloudy 46.8 49.3 52.8 547 54 54-6 56.1 58 

AVERAGES OF LEFT HAND GRIPS 

Month Oct. Nov. Dec. Jan. Feb. Mch. 

Clear Days 42.3 46.8 50.2 50.5 50.9 52.6 

Ptly. Cldy. 43.1 47.2 53-6 52.4 51-3 53-2 

Cloudy 42.6 46.2 49.4 51-8 50.5 52.5 

These tables show that partly cloudy days are the most 
favorable for muscle strength, that cloudy days are next, and 
that clear days are least favorable. In the three months, 
November, February, and May, it appears that cloudy days 
are slightly less favorable than clear days. An examination 
of the original data, however, shows that in November all the 
cloudy days were in the first half of the month, and as there 
was a large increase in November the seeming advantage of 
the clear days disappear. In May also, the only two days 
called cloudy, come in the first week of May so that the 
advantage of the clear days disappears here as well In 
February the low record for cloudy days is caused by low 
averages on two days, February 7 and 13, in the right hand. 
In each case the low daily average is due to a remarkably 
low mark by two boys of the group. During the months of 



Apr. 


May 


53.6 


55-4 


55-5 


57.3 


54.2 


55.8 



we:athe:r infi.ue:nce:s 79 

January, February, and March, it was not unusual for a bo}/ 
to drop from 3 to 5 Kg-, for a day or for a week, and as sud- 
denly recover his efficiency. The low marks above are such 
special cases. We are, therefore, justified in the conclusion 
that partly cloudy days are the most favorable to muscle 
strength, cloudy days next, and clear days least favorable. 

In the table for the Mental Tests, the advantage of the 
cloudy and partly cloudy over clear days is not so marked. 

MEMORY TEST AVERAGES 

Month Oct. Nov. Dec. Jan. Feb. Mqh. Apr. May 

Clear Days 9.4 10.4 10.8 ii.i 10 10.6 11.3 11.2 

Ptiy. Cldy. 10.2 10.4 II.I 10 10.2 10.2 10.9 II 

Cloudy Days 9.3 10.7 10.9 10.6 10.2 10.6 11.4 11. 5 

Here we see a small advantage for cloudy days in every 
month except January, and as in the muscle tests we find 
January, February, and March to be a time of unusual re- 
sults. The unusually high average for clear days in January 
is due to especially high scores on January 9, where two boys 
scored 15, and two 14; and on January 8, where one boy gol 
15, and three boys 13 points each. 

From the above data, therefore, we are warranted in con- 
cluding that cloudy and partly cloudy days are rarely a 
disadvantage, and that they may be positively advantageous 
to both physical and mental activities. 

(2) Temperature, Humidity, and Light Strength. 

In the tables where the weekly averages of the grip 
strength and memory records are compared with the weather 
variations, we find some variations in efficiency seem to be 
due to changes in temperature, humidity, and light strength, 
or to various combinations of them. In general, the results 
for muscle strength show a rising tendency in the fall as the 
temperature decreases, a period of arrest, while the tempera- 
ture is low, and a tendency to increase with increasing light 
strength from the first of March, which is aided by rising 
temperature from the first of April to the end of the tests in 



80 PERIODIC VARIATIONS IN KFFlClKNCr 

June. These are the same variations which Lehman and 
Pedersen found in their study. A question might be raised 
as to why Hght strength should not have influenced muscle 
strength earlier in the year. A glance at the tables, however, 
shows the reason why this is delayed. From the first of 
January to the last of February, we find only ii clear days, 
and a relative humidity of from 75 to lOO per cent, on all but 
four of the days during that time. This would indicate a 
long season of cold, damp weather, with a soft, and muddy 
soil, a time when the boys would not take much outdoor 
exercise, and when their vitality would probably be very low. 
That this is true is also shown by the fact that in this season 
of the year we find the only time when the average strength 
on clear days shows a superiority over that on cloudy days. 
It would further seem that cold weather with excessive hu- 
midity is unfavorable for muscle strength on account of its 
direct effects on the temperature of the human body. 

The data also show that while a moderately high humid- 
ity is favorable for temperatures of from 40° to 80° F., it is 
unfavorable when the temperature is below that point. Sev- 
eral instances may also be found in the records where a drop 
in the temperature accompanied by a rise in the humidity, 
caused a decrease in muscle strength, and an increase in 
memory ability. 

From a search among the individual records, we find 
that while the whole group did not lose in physical and 
mental efficiency at the same time, they all experienced a 
more or less pronounced slump sometime between the middle 
of December and the first of April. . Two of the ten began to 
slump in December, the other eight begining in January, and 
they all last from three to ten weeks. In the A. division, for 
the grips, five begin to slump in December, fourteen in Janu- 
ary, and three in February. 

It is very evident, therefore, that there are some causes 
at work which cause a decrease in physical efficiency during 



WEATHKR INFLUENCKS 8 1 

the months of December, January, and February, and two 
months of cold, cloudy, damp weather with low temperatures 
and high humidity, are undoubtedly among the causes. 



CHAPTER VII. 

CRITICAL REVIEW OF EXPERIMENTAL METH- 
ODS IN INVESTIGATING PERIODICITY 

(i) Introduction. We have seen that both mental and 
physical activities are far from being constant, and that 
there are many factors which seem to have a causal relation 
to them. While, as a whole, both the mental and physical 
tests show many irregularities, there are many rhythmic 
periods shown in the results. The causal factors which pro- 
duce these variations are sometimes very obscure. In addition, 
many other factors appear in an investigation of this kind 
which tend to produce variations in the data, such as ma- 
terials, procedure, methods of checking, and treatment of 
results. 

There are often so many peculiarities in the records for a 
group, that it is frequently difficult to account for them in any 
other way except individual differences. The following rec- 
ords for the week from March 13 to 17, all taken at 2 p. m., 
with little difference externally in temperature, or humidity 
(high on Friday), are typical of the results and show the 
difficulties in discovering causes by comparisons of varia- 
tions. 

Subject March 13 March 14 March 15 March 16 March 17 
Ba 433 10 435 12 345 12 456 15 2439 



Be 


4 


5 


6 15 


4 


4 


3 


II 


2 


2 


4 


8 


4 


3 


5 


12 


4 


3 


I 


8 


Ch 


4 


I 


5 10 


4 


5 


4 


13 


4 


4 


5 


13 


3 


4 


4 


II 


4 


5 


4 


13 


Cu 


3 


5 


3 II 


4 


5 


4 


13 


4 


2 


3 


9 


4 


4 


I 


9 


4 


3 


3 


10 


Fr 


4 


3 


3 10 


4 


4 


5 


13 


4 


2 


I 


7 


4 


3 


4 


II 


4 


3 


2 


9 


Ke 


4 


5 


3 12 


3 


I 


2 


6 


4 


2 


5 


II 


4 


I 





5 


2 


3 


3 


8 


La 


4 


3 


4 II 


4 


I 


5 


10 


3 


I 


2 


6 


4 


4 


4 


12 


I 


4 


I 


6 


Me 


4 


5 


3 12 


4 


5 


2 


II 


4 


3 


4 


II 


4 


3 


3 


10 


4 


4 


4 


12 


Mi 


4 


5 


4 13 


4 


3 


3 


10 


4 


4 


5 


13 


4 


5 


3 


12 


2 


5 


I 


8 


Ru 


4 


I 


I 6 


4 


3 


2 


9 


2 


3 


4 


9 


4 


2 


4 


10 


3 


3 


2 


8 



8^ 



CRITICAL R^VI^W '83 

'\ From the above results it would seem that unless we find 
a variation which is quite general, the cause is very difficult 
to discover except by statistical and graphic methods, and 
thus we are never sure whether similar variations show 
casual effects or not. No doubt the excessive humidity on 
March 17th contributed to the lowness of the mark, but the 
fact that it was on Friday, and St. Patrick's Day, may also 
have influenced the results., 

(2) Detailed Discussions of Scientific Meti^ods. 

In any experimental investigation concerning periodicity 
as shown in mental and physical tests, the chief things to be 
considered are : 

I — Adaptability of means to the end. This is one of the 
first requisites. Any neglect here is sure to prove a proHfic 
source of error. As a test of physical energy, the dynamo- 
metric tests seem to be one of the best as well as one of the 
easiest to make. The instrument used, the Smedley Dyna- 
mometer, is also admirably adapted to the use for which it is 
designed. Its light weight, as well as its adjustability make 
it an ideal instrument. 

As to the reliability of the mental tests, there is a great 
variety of opinion. Many sorts of tests have been devised, 
and after a careful study of the field, I have come to believe 
that numbers and nonsense syllables make the best materials 
for immediate memory reproduction. While the material 
may be criticised on the ground of conflicting associations, 
a conscious effort was made to avoid such associations in 
making up the materials. In addition to this, the numbers 
used are so commonly associated with their spoken name.-; 
that this association would seem to be dominant. Because of 
the limited time, and the ease of making them, tests for the 
immediate memory of a series of two place numbers were 
chosen as the material to be used in the tests. 



84 PERIODIC VARIATIONS IN F,FFICIKNCY 

Primary memory tests involve both attention and imme- 
diate memory, so that the presentation of the material is im- 
portant. Perhaps the presentation of the materials was such 
as to appeal more strongly to some types of minds than to 
others, but as the variations and not the actual score was to 
be used, this defect was largely overcome by a uniform pre- 
sentation of the materials. At best, mental abilities are very 
complex, and the validity of the results depends more on the 
uniformity of the materials, methods, and proceedure, than 
on any other factors, in making the tests. Immediate mem- 
ory is so universally depended upon in everyday life, that its 
importance for the mental life is second to none. We con- 
clude, therefore, that though the tests may be criticised, 
the same criticism may be applied to almost any sort of re- 
liable mental tests, and that the tests used are about as 
reliable as any tests yet devised. 

2 — Uniformity of Materials. While some of the tests may 
have been slightly more difficult than others, the differences 
were not great. This would perhaps account for occasional 
differences, of the whole group on different days, and for 
differences in the memory for the series of fours, fives, and 
sixes for the same day, but it could not account for such dif- 
ferences in the weekly record here given, where one boy's 
record is 4, 5, o, and anothers is 3, o, 6, etc., on the same day. 
As differences of this sort are much more common, we must 
conclude that differences in the materials caused little if any 
of the variations in the results. 

3 — Similarity of the Materials. There may perhaps have 
been some associations formed in the first series of four 
numbers which persisted until the second or third series, but 
a careful search in the original records shows only a few 
errors which could possibly be due to such associations. The 
elimination of all such associations is very difficult. Both 
Lobsien's and Gates' materials also suffered from the same 



CRITICAL REVIEW 85 

causes. While this defect might account for a few minor er- 
rors, the effects should not be over-estimated. 

4 — Time of the Year. Though the results of this investi- 
gation seem to show a course of seasonal periodicity, it is 
not pronounced. It is evident, however, from almost all 
studies, that there is a lowering of abilities beginning some- 
time between December and February, and that the periods 
from October to December, and from March to June, are 
more favorable than from December to March for mental 
abilities. This agrees practically with the low point in. the 
muscle tests, and shows there is some sort of relation be- 
tween them. In this test, also, the memory results do not go 
contrary to those for muscle strength as do Schuyten's and 
Lobsien's, but keep their level all through to the end of 
May. It may be true that the time of the year is not a real 
cause, but that the real causes are changes in temperature, 
light strength, air pressure, humidity, etc., but they are so 
closely related that for all ordinary purposes we may relate 
the variations in the results to the seasons of the year. 

5 — Time of the Week. Some investigators have found 
variations which seem to correspond to the time of the w^eek, 
though the results of this investigation do not seem to be 
much affected by it. The effects indicated seem to be due 
to other causes. 

6 — Hour of the Day. There seems to be no doubt about 
a diurnal course of efficiency, and it must always be taken 
into account by those who conduct investigations concerning 
mental and physical abilities. Its effects are quite apparent 
in the records shown during the first three months by the 
B. division. Early hours are never so favorable as later 
ones, and the maximum is usually found in the afternoon. 

7 — Temperature. Quick temperature changes, unseason- 
able temperature, and extremes in either direction seem to 
cause a drop in abilities, while slight changes seem to be 
beneficial. There are grounds for believing that each per- 



86 PERIODIC VARIATIONS IN EFElClKNCY 

son is affected in a unique way by variations in temperature, 
and that there is an individually varying optimum tempera- 
ture for each person. The bodily temperature is very closely 
related to outside temperature and is a resultant of outside 
temperature, humidity, exercise, ventilation, food, clothing, 
etc. 

In these tests temperature played a prominent part. All 
the tests were made in a large, light, airy room, with a ther- 
mostat set at 67° F., which regulated the temperature of the 
room. The heating and ventilating was controlled and reg- 
ulated by a combination of the plenum and exhaust systems, 
and three kinds of air — hot air, outside air, and air passed 
over steam jets to regulate the humidity. The temperature 
conditions in these tests were therefore fairly constant, and 
kept around 67° F. 

8 — Humidity. An excess of moisture or a lack of moist- 
ure in the air seems to be the cause of low efficiency in both 
mental and physical tests, though in this as well as in tem- 
perature, there seems to be an individually varying optimum. 
It must therefore be taken into account in any study on 
periodicity. 

9 — Air Pressure. A change in air pressure does not seem 
to produce much effect on either mental or physical activi- 
ties unless it is continued for a long time. 

10 — Fatigue. No doubt fatigue is an efficient cause in the 
variations of both mental and physical abilities. In this in- 
vestigation, however, I have tried to eliminate the influence 
of fatigue variations so far as possible, by giving short tests 
always at the same hour of the day. It is of course to be 
doubted that each individual was equally fatigued at the same 
hour each school day, but with only one record per day, we 
have no basis for discovering its influence. 

It appears from other studies that when the body tempera- 
ture increases above the optimum, the waste products are not 



CRITICAL re;vi£;w 87 

eliminated fast enough, and that they act as poisons, dimish- 
ing all activity and that fatigue then comes on rapidly. 
From the study of Gates, we see also that one's own ideas as 
to his abilities are not always reliable. The influence of 
fatigue, however, cannot be excluded from these results, but 
it must remain an unanalyzed factor in the diurnal course 
of efficiency. 

II — Daily Habits. Of course the ability of an individual 
may be influenced by many daily habits, such as the time of 
rising, time of eating, character and quantity of the food, 
clothing, general habits of work, etc., but in such a study as 
this, the effects of such influeaces are very difficult to dis- 
cover. 

12 — ^Practice Effects. In the physical tests, with growing 
youths for subjects, we see that the combination of growth 
and practice affects the results considerably. In this investi- 
gation, those who were tested five times weekly gained about 
twice as much at the same age, as those tested but once 
weekly. The mental tests, however, do not show these effects 
so plainly. It is probable that they are one of the chief causes 
for the fact that both muscle and mental abilities, when tested 
for any considerable time, show rising tendencies through 
the greater part of that time. 

13 — ^Exercise. While this is closely related to practice 
effects on the one hand, and fatigue on the other, exercise 
has an effect all its own. It is especially shown that physical 
tests taken before and after exercise show an increase in 
efficiency, and that rest after continuous work, either mental 
or physical, increases both mental and physical efficiency. 

14 — Other Individual Differences. There are many other 
factors involved in a study of mental and physical periodicity, 
such as age, sex, health, working habits, rest periods, sleep, 
endurance, pulse rate, blood pressure, etc., which may or may 
not influence the results from physical and mental tests. In 
these tests, where we must limit our study to mass results, it 



88 PERIODIC VARIATIONS IN EFFICIENCY 

is well to recognize possible causes even though we cannot 
point out their influence in any particular case. 

15 — Checking the Results. In any statistical study, the 
checking of the results is very important. When physical 
tests are given with a dynamometer, the results are at once 
expressed in a measurable cjuantity. It is otherwise with the 
results from the mental tests. In this instance, I decided to 
give a single point for each number correctly given in the 
proper order, one-half a point for a correct number in the 
wrong order, and one-half a point for each correct digit in 
the right place and order. 

The next question was which number series to count. The 
four series was good but too short. The five series was bet- 
ter, and the four series served as a sort of preparation for the 
five series. The six series was rather too long, but it gave 
an opportunity for those with high ability to use all of it. 
After considering the merits of each of the three series, I 
decided to use all of them, for though they were quite differ- 
ent, they were to be used for purposes of comparison. But 
I have given the weekly averages for each of the number 
series in the tables, and I have used them in making com- 
parisons with the weather. The results from all three prove 
to be very similar so that the use of the three series again 
justifies itself. 

16 — Uniformity of procedure. It is necessary to re- 
duce procedure to a basis of strict uniformity, for varia- 
tions in procedure may cause many accidental errors. 
Every investigator needs to have preliminary trials or tests, 
and work out the details of procedure thoroughly before 
starting the main tests upon which the results are to be 
based. The tests should always be taken or made by the 
same person, or serious differences may destroy the validity 
of the results. 

17 — Statistical treatment. In taking the physical abil- 
ities of a group, both the median and the average are 



CRITICAL RTi;vlT^W 89 

commonly used. The median may be valuable in testing 
a homogeneous group where the distribution of results is 
important, but in a group like the ones in this study, 
the variations are more important than the distribution. I 
have, therefore, used the averages. In the mental tests, the 
median is perhaps more important on account of the slight 
difference in ages, or in the study of a single test person. 
The median is given in some of the mental tables, but for 
the sake of comparisons, the main thing is uniformity of 
treatment, therefore, I have used the averages throughhout 
in making the comparisons. 

18 — Tabular presentation. The tabular presentation 
should be quite complete, showing as much of the detail 
of the data as possible. Tables should organize the data 
so that certain tendencies will appear plainly, and they 
should be used to illustrate the facts claimed to be dis- 
covered or proven by the investigation. The chief care, 
however, should be to give the complete data, so that others 
ma}' examine in detail and discover whether the conclu- 
sions drawn are warranted by the data. 

19 — Correlation of results. While a correlation ex- 
presses a certain mathematical relationship between two 
sets of data, from a great amount of work we get only a 
single mathematical expression which entirely neglects the 
details of the study. The value from such relationships is 
purely statistical, and the presence of a high correlation 
proves nothing. 

20 — Verifying Tests. It is always valuable when possible 
to conduct a series of verifying tests, in order to discover 
whether the results show general instead of special tenden- 
cies, and to prove the results of the real tests. In this in- 
vestigation, I can only use the records from the A. Divi- 
sion for that purpose. They show the same general ten- 
dencies as the results from the B. Division and tend to add 
to the value of the results. 



go PERIODIC VARIATIONS IN EFFICIJ:nCY 

(3) Validity of the Results. The validity of the re- 
sults depends almost entirely on the choice of means and 
materials, and on the degree of control exercised by the 
experimenter over the means, methods and procedure. 
In this case, the means were a typical group of high school 
boys of various ages. The method in the physical tests 
was one which has been used many times for similar pur- 
poses, and extreme care was used by the experimenter to 
keep the procedure uniform. The results from the physical 
tests are of unusual validity, and should be so considered. 

The means used in the mental tests, though open to 
criticism in minor points, are perhaps as well adapted to the 
purpose as any which had been devised up to the time when 
this experiment was made. It was necessary to have a 
series of mental tests that would not consume too much of 
the student's time, and one that would be of about uniform 
difficulty. Nonsense syllables were considered, but the task 
of making a sufficient number of tests, enough to last for a 
whole school year, in a short time, was too great, so num- 
bers were chosen. By using two place numbers, a series 
of three hundred 'mental tests was made from materials 
which are so common that associations between the num- 
bers were lost from one day to another, and in this way 
each series was entirely new when presented. Then again, 
the results from the memory tests are not expected to set 
standards of mental ability, but to furnish data for com- 
parisons. They can therefore be used for that purpose to 
good advantage, and for purposes of comparison, the re- 
sults are perfectly valid. 



CHAPTi:R VIII. 

SUMMARY AND SUGGESTIONS 

The following sigriificant facts concerning periodicity 
seem to be indicated by the results of my investigation : 

(i) There are three distinct periods in the physical 
strength of growing boys in the course of a school year, a 
period of growth from September to about the middle of 
December, a period of depression from January to March, 
and a period of renewed growth from March to June. 

(2) There are also three more or less distinct periods in 
mental energy during the school year, the curve of which 
tends to resemble the curve for physical periodicity in the 
same group of subjects: first, a favorable period from 
September to the end of the year, an unfavorable period 
from January to March, and a second favorable period 
irom March to May. 

(3) The depression in mental abilities seems to appear 
somewhat after the depression in physical strength, is much 
less noticeable, and does not last so long. 

(4) The period of depression in mental and physical 
abilities comes at the beginning of winter, and while it 
shows many individual variations, it occurs in all subjects 
studied and lasts from three to six weeks. Adults and boys 
of low vitality tend to show it early in December. Young 
and growing boys show it any time between the first of 
December, and the middle of January. In some subjects the 
effects are overcome by the middle of February, in others by 
March, but in special cases it sometimes lasts until ]\Iay. 

(5) Sunlight seems to affect mental and physical abili- 
ties favorably, the stronger its rays, the more its influence. 

(6) Temperature has an individually varying optimum, 

91 



92 pe;riodic variations in efficiency 

so that both the lowest and the highest temperatures have a 
depressing effect. 

(7) The larger yearly periodic variations in mental and 
physical abilities are probably due in a large part to the com- 
bined influence of temperature and light strength. 

(8) Other causal factors in periodicity are food, cloth- 
ing, body temperature, humidity, air pressure, character of 
the day, fatigue, time of day, practice effects, previous men- 
tal and physical development, mental activity toward the 
activity tested, general bodily health, and various individual 
differences. 

(9) Changes in temperature and humidity are at first 
seen in the changed body temperature. When long con- 
tinued, they clearly affect both physical strength and mental 
abilities. 

( 10) There is nothing in the twenty-eight day periods 
of Malling-Hansen, or the twenty-three day periods of 
Fleiss-Svoboda. 

(11) There is no distinct weekly periodicity as shown in 
the mental and physical tests. While Monday seems to be 
more variable than the other days of the week, in general, 
the changes which appear from day to day seem to be due to 
other causes than merely the time of the week. 

(12) There is a distinct diurnal course of efficiency 
shown in both the mental and physical tests. Both increase 
quickly through the forenoon, each show a slight decrease 
around noon, and both come to a maximum in the afternoon. 
That for mental abilities culminates around 2 p. m., while 
that for physical abilities often comes later in the afternoon. 

(13) Cloudy and partly cloudy days, if not too long con- 
tinued, are usually more favorable to both muscle strength 
and mental efficiency, than clear days. Cold, cloudy weather 
with a high humidity, when continued through several days, 
is unfavorable to both mental and physical abilities. 



SUMMARY AND SUGGKSTIONS 93 

(14) In general, the cyclonic movements of the air which 
precede a storm, seem to be favorable to muscle strength, 
while the anti-cyclonic air movements which follow, seem to 
have a depressing effect. 

(15) The existence of an individual optimum in tem- 
perature, in air pressure, and in humidity, which is most 
favorable to mental and physical activities, is very im- 
portant, and should be further investigated. 

(16) Most of the investigations in this field are suf- 
fering from the effects of statistical treatment of the facts. 
Many times, more can be learned from the careful study of 
one subject than from the statistical treatment of the re- 
sults from a large number of subjects. 

(17) There is need of many careful experimental studies 
on the influence of various climatic conditions and atmos- 
pheric changes on individuals. 

(18) There is need of many more investigations con- 
cerning both mental and physical periodicity where the con- 
ditions are carefully controlled. 



CHAPTe:R IX. 

BIBLIOGRAPHY 

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4. Burke, Frederick. American Journal of Psychology, April, 
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5. Burnham, Wm. H. Optimum Temperature for Mental Work. 
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6. Christopher, W. S. Report on Child Study Investigation. 
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7. Dexter, E. G. Conduct and the Weather.. Psych. Review 
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10. Finsen, N. Om Periodiske aarlige Svingninger i Blodets 
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11. Gates, Arthur I. Variations in Efficiency During the Day, to- 
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12. Gates, Arthur I. Diurnal Variations in Memory and Associa- 
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13. Gulick, L. H. Discussion of Report of Committee on Variable 
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14. Hall, G. Stanley. Adolescence, Vol I. p. 21-23. 

15. Hall. Winifred. Psychological Bulletin, 1909. 

16. Harley, V. The Effects of Sugar and Smoking on Muscular 
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17. Hill, L. Stuffy Rooms: facts and fancy about ventilation 
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94 



BIBLIOGRAPHY 95 

20. Krsepelin, E. Zur Hygiene der Arbeit. Zeitschrift fiir 
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21. Kuhnes, L. L. Variations in Muscular Energy. An unpub- 
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22. Lee, F. S. The Effects of Temperature and Humidity on 
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23. Lee, F. S. The Recent Progress in our Knowledge of the 
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24. Lehman, A. Die Korperliche Ausserungen Psychischer Zus- 
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25. Lehman, A. and Pedersen, R. H. Das Wetter und Unser 
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26. Lobsien, Marx. Schwankungcn dcr Psychischcn Kapazitat. 
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27. Lobsien, Marx. Experimentelle Untersuchungen liber die 
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28. Lombard, W. P. Some Influences Affecting the Power of 
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29. Malling-Hanscn. Perioden im Gcwicht der Kinder und in der 

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30. Marsh, Howard D. The Diurnal Course of Efficiency. Arch, 
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31. Meumann, Ernst. Vorlesungen, Vol. L 

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34. Robinson, L. A. Mental Fatigue and "School Efficiency. 
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35. Schuytcn, M. C. Influence dcs variations de le temperature 
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IJAcad. Roy. des Sciences, des Lettres, et des Beaux Arts de 
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36. Smith, E. Analysis of Respiration. Proceedings of the Royal 
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37. Storey, T, A. Studies in Voluntary Muscular Contraction. 
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39. Svoboda, L. Cited by Peters, V. Zeitschrift fiir Psychology. 
1913. p. 614. 



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